Fixed error of selecting tool twice, added object `model`

Tool on control panel cannot been selected twice anymore, because
second click unactivate tool now. `Model` object that holds tables
(and in the future `relations` too) and methods for its creating is
now part of application.
Added creating of relation, fixed styles structure, added table id
attribute

Prepared creating relations between tables, only missing really create
new relation. Directory structure for `styles` was edited to be same
as in the `test` and `src` directories. Created tables now have `id`
attribute used for their identification.