This commit will add the ability to create a new document.
A FAB is used in home screen which on expansion gives
four options namely new writer document, new impress,
new Sheet or new Draw. Two new events loadNewDocument
and saveDocumentAs have been added.
Another major change includes the use of constraint layout
in LOUIActivity layout as it decreases nesting of views and
improves the app performance. This was needed because
of the new FAB layouts being added.
Support for vector drawables has been enabled.

Change-Id: Ia3ea17f73c0d8514f8ddb7b9a1cbd2ce7de6ac08
Reviewed-on: https://gerrit.libreoffice.org/35183Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>