Edit tags in place

[Mathias Brodala]

Exaile could optionally offer a way to edit track tags in place. Suggestion:

1) User has to keep pressing the [Alt] key to trigger editing mode. ([Strg] and [Shift] are already reserved)
2) All selected tracks will have their current value of the currently edited tag overwritten with the new value.
3) A confirmation is displayed after editing (possibly via GtkInfoBar or something else unobtrusive.)
4) The confirmation offers ways to undo the last change to fix inadvertent changes.

Even though the confirmation can catch quite a lot of problems, this should be optional. Thus a plugin or a setting in the core should be activated first to use this.

[Johannes Sasongko (sjohannes)]

> 1) User has to keep pressing the [Alt] key to trigger editing mode. ([Strg] and [Shift] are already reserved)

An alternative is to use a key trigger, e.g. F2. But you'd have to
come up with a way to switch between columns (Tab?).

[Mathias Brodala (mathbr)]

A few ideas collected through #exaile:

1) It is most likely preferable to switch to a special editing mode upon pressing the editing key (F2 is preferred, long single left click could be available as an option).

2) In that mode one can switch between columns via Tab and Shift-Tab.

3) In that mode one can freely navigate between columns and rows via Alt+<Arrow> (<Arrow> being Up, Down, Left or Right)

4) In that mode one can directly jump to a column via Alt+<#> (<#> being 0..9)

5) All changes are undone by pressing the Esc key. This also exits from the editing mode.

6) Changes can be undone in place