Extend the interface of ScriptRepository for removing files

Add two new methods to ScriptRepository to allow removing files locally
and from the central repository.

re #7031
Definition of the unit test for removing methods

Creation of the unit test to ensure the functioning of removing files
locally and remotelly.

re #7031
Implementation of removing files ScriptRepository

Implements the remove and remove_local methods.

re #7031
local empty folder returns status remote_only

a unit test to trigger this effect.

re #7031
Solve the issue of empty folder

It also allows removing local folders recursively

re #7031
Provide the delete functionality to RepoModel

Extend RepoModel to support the delete entry functionality.

re #7031
Add trash icon to Mantid

It will be used for the delete functionality.

re #7031
Delegate to Delete functionality

extends ScriptRepositoryView to provide interface to delete functionality

re #7031
Improve the delete functionality

This commit deals with 2 points:

 * when you upload even small files it seems quite slow before the icons tells you it is done:
   * It is still slow the interection with the server.But now, it updates the icon as soon as the upload thread finishes.
 * After deleting the icon still tells you the file is up to date on the repo.
   * This used to occur if the user clicked on reload button while uploading. Now, this button is disabled.

re #7031
Change the requirement for deleting entries from ScriptRepository

Request "Get rid of the local file deletion. I don't think users will expect this, make delete only delete from the repository."

The script repository will not remove files locally. The ScriptRepository.h
indicates this change and ScriptRepositoryTestImpl.h translate the current
requirement on removing entries from repository.

re #7031
Implement the new requirement for deleting entry

re #7031
Adapt the RepoModel to the new requirement on deleting entries

re #7031
Allow the ScriptRepository Widget to be resized in a better way.

re #7031
Improve responsiveness and fast change the icon

Sometimes it used to take much time to change the icons of upload/donwload
trash, working and so on. It was a problem of emiting the indexes.

Now the connection is better. And the icons changes as soon as the upload,
delete, download are finished.

re #7031
Merge remote-tracking branch 'origin/feature/7031_deleting_scripts'

Conflicts:
	Code/Mantid/MantidQt/API/inc/MantidQtAPI/ScriptRepositoryView.ui

Refs #7031