CORE-3935 Refactored unshare list in SharePanel.

Rather than maintaining an unshareList, the SharePanel will now remove user entries from its sharingMap on unshare actions, then compare the user entries in the original list to the maintained sharingMap in order to build an unshareList in the getUnshareList method.
This prevents the bug where a user cannot be re-added once they were removed from the grid.
This approach will also prevent unshares errors when a user is removed from the grid, then re-added with different permissions (since the displayed permission was also checked by the removed isExistedOriginally method via the DataSharing::equals method).
CORE-3922 Hide SelectCollaboratorsDialog before removing Handlers.

Prevents the dialog from remaining open if a potential "redundant remove" exception is thrown.
CORE-3922 Added extra space around Unshare action in SharePanel grid.
CORE-3939 Enabled Share when only 1 folder selected.

Updated DataUtils::getSupportedActions to include the Share Action when any item is selected.
CORE-3936 Added DataLinks Action to DataUtils.

Added a hasOnlyFolders method that is checked in the getSupportedActions method to determine if the new DataLinks Action should be included in the returned list.
Added a check for this Action in the DataActionsMenu to determine if the Manage Data Links menu item is displayed.
CORE-3940 CORE-3943 Improved sharing labels and instructions.

Updated button text for adding and managing collaborators in the SharePanel and the SelectCollaboratorsDialog.
Updated the empty text in the SharePanel grid and the SelectCollaboratorsDialog grid.