feat: variable support in numerous actions and feedbacks

[JaaHann]

Added variable support via toggle on following actions:

• Go forward (n) clips
• Go backward (n) clips
• Shuttle with speed (resolving #96)
• Play (resolving #48)

Added direct variable support on following actions:

• GOTO (TC) (resolving #82)
• Jog backward (TC) duration
• Jog forward (TC) duration

Added variable support on following feedbacks:

• Active clip
• Active slot
• Slot/disk status

Added "parseOptNumber" function to "actions.ts" to parse a number from textinput with variables from options object. Added "parseOptString" function to "actions.ts" to parse a string from textinput with variables from options object.

[JaaHann]

Done! Thanks a lot, I thought about that on the "isVisible" logic but still forgot the same issue in the callbacks...