Enhancement: Create a new space

A new floating action button has been added to the spaces list, visible only to users with right permissions.
In addition, a new dialog for space creation has been implemented and, it is shown when the floating action button is tapped.

https://github.com/owncloud/android/issues/4606
https://github.com/owncloud/android/issues/4688
https://github.com/owncloud/android/pull/4683
https://github.com/owncloud/android/pull/4694
