The outline needs some space outside the element. This space may be more
than the parent has (when the element is positioned right at the edge).
When this happens we simply ignore that 1 pixel space. Everything still
shows correctly.

This needs a z-index on the selected section, since the outline collides 
with other sections and is not shown on this side.

Use proper types and remove unused vars.

The main components are right at top level and the directories below
mimic the data structure (unit->page->section).
The toolbar is only used in dev mode and does not belong directly to the
unit view.
The TextEditor is a complex component and deserves it's own directory
even though it is used within the unit-view. Might be refactored to its
own module later.

- The selection service only needs to handle element selection. For
pages and sections having the index is enough.
- Those indeces are simple fields instead of observables. This also
simplifies the components which don't have to get the value out of the
observables.
- Therefore the selection service does no longer need to have a direct
reference to the unit service and it's unit.
- Selection logic is not done by the section components themselves but
by the parent canvas component.
- The unit service can now manipulate pages and section by index in
addition to passing the necessary objects directly.

And having the correct grid coordinates.
Also refactored the canvas sections to be different components.