Create prototype of toolbox widget as described in #27.
Enhance Toolbox with tool choosing properties.

Toolbox now should be able to serve its main purpose as requested in #27.
Add Toolbox widget to the main window (and close #7).

Toolbox is working as an essential part of the application.
However, so far it comes with very basic tools and capabilities.
More features should be provided and addressed in further issues.
Merge branch 'master' of https://github.com/mkacz91/apricot