wx GUI: Improve code
wx GUI: Don't process Tab in the editor text area by default

Addresses #352
wx GUI: Temporary fix for #331
wx GUI: Temporarily work around bug #332
wx GUI: Don't Tab-traverse editor plugins' widgets when panels are collapsed

Fixes #353
wx GUI: Allow expanding/collapsing editor plugin panels with Space or Enter

Fixes #333
wx GUI: Highlight plugin panel bars when focused
wx GUI: Simplify code
Core: Simplify code
wx GUI: Simplify code
wx GUI: Improve code
wx GUI: Improve code
wx Copypaste: Restructure code
wx Tasklist: Add Alt accelerator
wx DBsearch: Add Alt accelerator
wx GUI: Introduce AcceleratorsManagers class
wx GUI: Alternative movement keys
wx GUI: Main focus accelerators
wx GUI: Notebooks accelerators
wx GUI: Database accelerators