Status Icons: Rename the syncEnable method to isPaused.

Previously, in folder and folderman there have been the syncEnabled
properties, but they confused the semantics: While in FolderMan the
syncEnabled flag represents the network connection and stuff, in
Folder it represented if the user paused or resumed the folder.

This resulted in mixed use of both, which lead to wrong icon states.
This patch renames the folder methods and properties to isPaused to
make more clear about what it is.
Status Icons: Let FolderMan only write the folder config files.

Remove the setSyncEnabled() call to individual folders which mistakenly
set the folders to pause. Let the folders keep their pause state on their
own.

If FolderMan is set to be enabled emit a general refresh signal rather
than one for each folder.
StatusModel: Have another property accountConnected.

With that , make the status model aware of the account connection state.
With that, we can grey out the correct state icon if the account is not
connected and display the normal icon if the account is connected.
Some minor cleanups.
Status icons: Set the offline icon at the very beginning.

Otherwise, if the account is signed out and opens the credential popup,
there is a wrong icon displayed. If the account is coming from keychain
this icon is quickly overwritten.
Status icons: Display the correct icons after startup connect.
Propagator: If the sync was interrupted by pausing, do not show error.

Handle problems which happen because of pausing the sync as soft errors
rather than normal errors which are blacklisted and displayed in the
gui.

This fixes bug #1959
Status Icon: Set a proper icon if no sync is configured.

This fixes bug #1956
Merge pull request #2075 from owncloud/use_folder_paused

Rework of the status icons in FolderMan and Folder objects.