Add Slack corporate import ability (#10905)

* add support for slack corporate export data

* changed tempChannels for channel types. concat after parsing channels

* fix typo

* add fixes suggested by @lieut-data

tests/slack-import-test-direct-messages.json

@@ -0,0 +1,34 @@
+[
+    {
+        "id": "D24TJMP61",
+        "created": "1472131245",
+        "members": [
+            "U1VVY70HK",
+            "U1W4XLR62"
+        ]
+    },
+    {
+        "id": "D24TJNXUG",
+        "created": "1472132335",
+        "members": [
+            "U1XG9JUH1",
+            "U20APGU90"
+        ]
+    },
+    {
+        "id": "D24TLE5V5",
+        "created": "1472131113",
+        "members": [
+            "U1TQ3A3L7",
+            "U1URR19QV"
+        ]
+    },
+    {
+        "id": "D24TM4MPT",
+        "created": "1472131021",
+        "members": [
+            "U1V47GAM9",
+            "U1XVNP6DT"
+        ]
+    }
+]

tests/slack-import-test-group-direct-messages.json

@@ -0,0 +1,69 @@
+[
+    {
+        "id": "G1XSSNBTP",
+        "name": "mpdm-mcauly--sutton--barker--lankford-1",
+        "created": 1470239933,
+        "creator": "U1FFMLSKC",
+        "is_archived": false,
+        "members": [
+            "U1934896U",
+            "U1TTSPAGP",
+            "U1FFMLSKC",
+            "U1U234D4P"
+        ],
+        "topic": {
+            "value": "Group messaging",
+            "creator": "U1FFMLSKC",
+            "last_set": "1470239933"
+        },
+        "purpose": {
+            "value": "Group messaging with: @mcauly @sutton @barker @lankford",
+            "creator": "U1FFMLSKC",
+            "last_set": "1470239933"
+        }
+    },
+    {
+        "id": "G22KV02G2",
+        "name": "mpdm-mcauly--wolfgram--weddington-1",
+        "created": 1471532476,
+        "creator": "U1K9SEY9K",
+        "is_archived": false,
+        "members": [
+            "U1934896U",
+            "U1K9SEY9K",
+            "U1YTGR5CP"
+        ],
+        "topic": {
+            "value": "Group messaging",
+            "creator": "U1K9SEY9K",
+            "last_set": "1471532476"
+        },
+        "purpose": {
+            "value": "Group messaging with: @mcauly @wolfgram @weddington",
+            "creator": "U1K9SEY9K",
+            "last_set": "1471532476"
+        }
+    },
+    {
+        "id": "G2436812A",
+        "name": "mpdm-mcauly--lovell--buck-1",
+        "created": 1471964085,
+        "creator": "U1934896U",
+        "is_archived": false,
+        "members": [
+            "U1934896U",
+            "U1YYZNDJP",
+            "U1JSZSPR7"
+        ],
+        "topic": {
+            "value": "Group messaging",
+            "creator": "U1934896U",
+            "last_set": "1471964085"
+        },
+        "purpose": {
+            "value": "Group messaging with: @mcauly @lovell @buck",
+            "creator": "U1934896U",
+            "last_set": "1471964085"
+        }
+    }
+]

tests/slack-import-test-private-channels.json

@@ -0,0 +1,25 @@
+[
+    {
+        "id": "G1T7B1T9N",
+        "name": "csi-team-chat",
+        "created": 1468959839,
+        "creator": "U17G57PB6",
+        "is_archived": false,
+        "members": [
+            "U15CML9C1",
+            "U1934896U",
+            "U17G57PB6",
+            "U1T7A2J56"
+        ],
+        "topic": {
+            "value": "\"A constantly evolving landscape of hills\"",
+            "creator": "U1934896U",
+            "last_set": "1469017133"
+        },
+        "purpose": {
+            "value": "CSI team chat",
+            "creator": "U17G57PB6",
+            "last_set": "1468972624"
+        }
+    }
+]