Make the proof tree (or the KeY GUI in general) responsive during automatic proof search

[wadoon]

Fixes #3415.

State:

• Glasspane removed
• KeyAction classes extended for enabledness updates
• Look through actions and decide whether they are safe or not to be executed during auto-mode.

[wadoon]

State of this PR:

In this PR the GlassPane blocking the user input was removed. Instead of this overall deactivation, each action must be de-/activated. A new facility was introduced to KeyAction. KeyAction holds a predicate function () -> Boolean which defines its enability. KeyAction#updateEnabledness updates Action#setEnable accordingly to this function. This method should be used in listeners (property change listeners, etc...) to update the value.

MainWindowAction exploits this facility with two methods, which setup the listener and predicate function accordingly:

• #enabledOnAnActiveProof();: Action is enabled if a proof is selected
• #enabledWhenNotInAutoMode();: Action is not enabled if the main window is in "auto mode".

It is possible to call both methods, then the condition is conjunctively joint.

Note, that this PR requires manual testing and clicking within the GUI.

[wadoon]

Review requested for two months. I rebased and fixed formatting to finally abandon this PR.

@mattulbrich @unp1