Engine: implement "accessibility" config for speech and text skip

[ivan-mogilko]

Per a very old users request.

This allows players to override game's speech skip style to their preference if the game does not provide such option.

Adds two config options under "[access]" group:

[access]
speechskip = <none, input, any, time>
textskip = <none, input, any, time>

Both may take following values:

• "none", or empty string (default) - this actually means that the option is not used
• "input", meaning any player input
• "any", meaning any player input, or time
• "time", meaning time only

These options override in-game settings for skipping speech and displayed messages respectively.

The override is done:

• when the game is loaded
• when the save is restored (because these options may be saved)
• when these options are changed by a script, these overriding settings may prevent assignment of a new value.

Note that reading a Speech.SkipStyle property in script will actually return a true overridden value. This is done in case game script uses this property as a reference when implementing custom speech, for example.

[ivan-mogilko]

Alright, I'll merge this, although I never got a response from a user who asked for this recently. But this works, and might work as a workaround.

Ideally these settings should be in winsetup, I think. But winsetup is badly designed (ui-wise), and should be either transformed into multi-paged window with tabs (short term), or completely rewritten into something cross-platform (long term).