Rebar intergration and boss_compiler changes

1. boss_db_rebar plugin: I've changes return status of compile_model/4 to rebar_base_compiler:ok_tuple and rebar_base_compiler:error_tuple, now rebar gives nice info on compilation error.

2. boss_compiler: IncludeDirs variable is  building from default app "include" dir, 'include_dirs' option and all 'i' tuples, so aleppo doesn't complain about missing includes.