EP128: integrate EP128 target (ex-Xep128 project) into the Xemu framework fully

[lgblgblgb]

Original project ("rough" integration with MANY private solutions with the now historical ticket of #171 , this issue is now about a "proper" integration!!!)

Historically, my EP128 emulator was an full stand-alone, single-emulator project, called Xep128. Many of its solutions was then building block of the Xemu project, but far from being all. Also since then Xemu evolved much more. Xep128 has been integrated later into the Xemu project as the EP128 target, but still many of its solutions are kept as-is, thus making serious problems not so well integrating into the Xemu project. This must be solved. Also, there can be a few Xep128 specific solutions which are not available in the Xemu framework yet, and would be useful in general for other targets (so the opposite of this problem above ...).

#161 belongs here, too.

[lgblgblgb]

Work in progress, partial results: 7f34465 and 8210a59

[lgblgblgb]

So far:

• rendering/updating/timing + OSD is migrated to Xemu fw (fw = framework)
• keyboard handling is on xemu fw now, joystick/mouse emulation MAY not work the same way though (TODO: testing, fixing)
• console is on Xemu fw (consider: having Xemu fw extended for console input)
• command line + cfg parsing is on Xemu fw (now some options are missing ... also kbd definition is different)
• file handling is on Xemu fw, thus pref.dir is different now

[lgblgblgb]

We have UI context stuff as well now for EP128: 1e52ebe

As a side effect, some generic UI CBs are ported to the framework level to be used with other targets as well besides EP128.

[lgblgblgb]

OK, now I guess it's OK to close this :) Further enhancements are not so much scope with the integration any more.