Implements DBus methods for manipulation of splits

Methods implmented allow for:
1. retrieval of layout information encoded in a string
2. getting size proportions of a splitter's direct child widgets
3. setting the size proportions of a splitter's direct child widgets
4. simple splitting of a view horizontally or vertically
5. using existing widgets to create a splitter at a specified position under a splitter
6. moving an existing view to a specified position under a splitter
7. moving an existing splitter to a specified position under a splitter
8. switching focus to an existing view

See documentation in source files for more details.

BUG: 465448