New keyboard commands: Play at selected timestamp + Play X secs before selected line

[porg]

New keyboard commands

• Two new shortcuts as the counterparts to the respective mouse interactions:
  • Mouse interactions: More differentiated operation #111
• Function: Play at selected timestamp
  • ⌥ -⏎ with ALT on macOS generally being used as the modifier key for an alternative/opposite function
• Function: Play X secs before selected line
  • ⇧-⏎ with the mnemonic being: "Playback at upper line" just like the Shift key which is an arrow pointing up, and which is at a more upwards position then the other modifier keys.

Note

• The shortcuts have to be assigned to remain consistent and useful with the existing shortcut keys.
• My proposals above where proposals within that existing convention.
• If you re-assign play/pause too, then this can be altered more freely or more finger-friendly.