PLT-3782 Do not move the "@" sign and flag icon to the left of search bar when opening the right hand sidebar (#4850)

* do not move the mention & flag button to the left of the search box when in search mode

* fixed the margin & padding issues of the search box

* fixed the member icon positioning issue and the expanded sidebar toggle issue

* fixed remaining bugs when sidebar is in expanded mode

* changed propTypes from func to bool

webapp/components/channel_header.jsx

@@ -728,12 +728,12 @@ export default class ChannelHeader extends React.Component {
                                     </OverlayTrigger>
                                 </div>
                             </th>
-                            <th>
+                            <th className='header-list__members'>
                                 {popoverListMembers}
                             </th>
-                            <th className='search-bar__container'><NavbarSearchBox/></th>
+                            <th className='search-bar__container'><NavbarSearchBox showMentionFlagBtns={false}/></th>
                             <th>
-                                <div className='dropdown channel-header__links'>
+                                <div className='dropdown channel-header__links search-btns'>
                                     <OverlayTrigger
                                         delayShow={Constants.OVERLAY_TIME_DELAY}
                                         placement='bottom'
@@ -750,7 +750,7 @@ export default class ChannelHeader extends React.Component {
                                 </div>
                             </th>
                             <th>
-                                <div className='dropdown channel-header__links'>
+                                <div className='dropdown channel-header__links search-btns'>
                                     <OverlayTrigger
                                         delayShow={Constants.OVERLAY_TIME_DELAY}
                                         placement='bottom'