Move some VisEditor UI utilities to VisUI

[kotcrab]

Followed from #168.

• [x] AsyncTask API and AsyncTaskProgressDialog

To be considered:

• VisChangeListener - allows to use ChangeListener with lambdas, perfect for Java 8 users
• EnumSelectBox - select box for enums, support custom enum names
• ProgressImage - spinning image with round progress icon
• IndeterminateCheckbox and IndeterminateTextField - checkbox and text field that can be set into indeterminate mode. Unlikely though, implementation is pretty specific.

[mbrlabs]

Moving the AsyncTask API to VisUI would be great, that's exactly what i would need. Are you still planning on doing that?

[kotcrab]

@mbrlabs eventually yes, if you need it asap you can copy util/async package and AsyncTaskProgressDialog class. I'll take a look at it tomorrow if I find some time.

[mbrlabs]

Cool, thank you. But you can take your time, it's not really important right now. If it ends up in the 1.2.5 release that would be great. Otherwise i just copy the package.

[kotcrab]

@mbrlabs I've moved it, you can try it in latest snapshot.