rm BA_CORE_API_ from GUI classes; initialize static const members in header file
- ignore directories tidy, cover; they are meant for clang-tidy and coverage tests
- rm BA_CORE_API_ from GUI classes
- initialize static const members, namely the M_* T_* and P_* string constants in GUI item classes, in the header files; this resolves a clang-tidy warning about static initialization order fiasco.