Clean up BR_Envelope a bit
BR_MouseContextInfo updates
+Renamed to BR_MouseInfo
+Added ability to get envelope point id under mouse
+Updated the way modes works
Added actions (closes #124)
- SWS/BR: Delete take under mouse cursor
- SWS/BR: Select TCP/MCP track under mouse cursor
- SWS/BR: Select envelope under mouse cursor
- SWS/BR: Select/Delete envelope point under mouse cursor (2 versions: selected envelope only and whatever envelope is under mouse cursor)