PLT-1316/PLT-3280 Change client-side max file size limit (#3354)

* Change client-side max file size limit

It now relies on the value set in config.json.
Re-enable and tweak the max file size setting in system console.

* Update file upload error message

webapp/components/user_settings/user_settings_general.jsx

@@ -95,6 +95,7 @@ class UserSettingsGeneralTab extends React.Component {
         this.updateSection = this.updateSection.bind(this);
 
         this.state = this.setupInitialState(props);
+        this.setState({maxFileSize: global.window.mm_config.MaxFileSize});
     }
     submitUsername(e) {
         e.preventDefault();
@@ -221,7 +222,7 @@ class UserSettingsGeneralTab extends React.Component {
         if (picture.type !== 'image/jpeg' && picture.type !== 'image/png') {
             this.setState({clientError: formatMessage(holders.validImage)});
             return;
-        } else if (picture.size > Constants.MAX_FILE_SIZE) {
+        } else if (picture.size > this.state.maxFileSize) {
             this.setState({clientError: formatMessage(holders.imageTooLarge)});
             return;
         }