non-session-manager support

Implements open, save and dirtiness.
No error checking, no menu items disabling.
Prevent the new session dialog from appearing
Make sure every imported file is copied to the session path
Better start up

Don't reply to nsm server until ardour project is finished loading
Disable some actions that are not allowed while under nsm
Merge branch 'nsm' of https://github.com/royvegard/ardour
fix up iterator syntax and unnecessary use of X_() in NSM patch
clarify comment about Automatable/ControlSet inheritance
likely fix for #5426 (hide all tracks doesn't work and causes inconsistent state
fix #5424: routes created from templates do not get names based on the user-supplied text from the add route dialog
vtl: draw cross if info-request fails in open-video preview.
vtl: update video-export

* range: pre/postfix with black video-frames
* fix A/V offset - decode and skip source until offset is reached
* use spinning progress-bar during decode&skip
* use video-stream index in stream-map
* fix audio-export abort; stop freewheeling
* re-indent code
vtl: update export information
vtl: remove xjadeo option dialog

xjadeo options (selective session restore) are only
useful for testing and debugging.
vtl: remove video-maintenance menu

* only really relevant for testing/debugging.
* the back-end functions are still used for 'normal' operation
  and called implicitly when opening/closing a video.
* call stop_video_server() when removing a video.
vtl: update session start/end only when adding (or dragging) the video
Don't wait for session_is_loaded from nsm server
Forgot to clean up nsm.* in previous commit
fix (?) behaviour when punching into automation write mode while the transport is moving, hopefully without breaking anything else
Merge branch 'master' of git.ardour.org:ardour/ardour