Fix for #354 - wrongly calculated widget sizes.

[and3md]

This PR improve DlangUI widgets measure and window content support. Now it's possible to do something like this:

Widget measure

This can't be done without change some widget measure behavior. Now widgets are increasing when has FILL_PARENT flags - not shrinking to window size. We must measure widget size not content size for some of widgets like Grid, TreeView, EditBox, EditLine. Most of this widgets need optimizations - content size can be measured only when content is changed. I don't do that in this PR.

ScrollWidgetBase and inherited

I added minimumVisibleContentSize() which is used to get minimal sensible size.

EditLine

I deliberated long time how to do it. And I think the best way is to get width and height of some standard text. I used "aaaaa" but there is _textToSetWidgetSize and in the future we can add property to set it to something else. Using string gives certainty that changing font will make widget enough big.

That fixes not only getting minimal size but also widget don't grow when you write letters in some cases (for example when there are 2 widgets in horizontal layout with FILL_PARENT flag in one line).

EditBox

Analogous to EditLine but it uses "aaaaa/naaaaa". There should be minimum 2 lines of text.

ListWidget

This is a little tricky because it is used for menu. First measure returns 100,100 second measure returns real size (only because of menu).

WindowOrContentResizeMode enum

I not found better name, maybe someone gives something shorter.
There are three algorithms:

• shrinkWidgets - something like in previous version of DlangUI
• resizeWindow - window is resized to fit content (not working in X11 now because Window.windowResize() is not implemented in X11
• scrollWindow - now default, if widgets are bigger than window adds scrollbars to window

Warnings

1. I tested this solution on Linux and Windows (X11, SDL, win32 platforms).
2. Tested with example1, DlangIDE and my own project
3. Some windows may need some tweaks because now widgets are increasing when has FILL_PARENT flags not shrinking to window size. Usually some layouts needs set FILL_PARENT flag.
4. Need more tests.

Extra fixes

Fixed theme change on X11.

[buggins]

let me review it...