Adding RTL support

[widmoser]

Adds right-to-left support for ui layout containers. This will automatically work as long as the ui-layout element is a child of an element with a direction set to rtl.

Fixes issue #168.

[widmoser]

Tests are still missing. Every test should be also replicated in RTL mode.

[SomeKittens]

Initial scan looks alright. Will give a full review when tests are added.

[SomeKittens]

Why was this change made?

[widmoser]

I removed the dependency of the code on the flow property variable. It only remains when setting the css. For one, this is a refactoring step that makes the code more readable in my opinion. But more importantly it is also more robust, because the position keeps being valid even if the flow property changes (in case the layout is switched to RTL for example). Without this change the position is stored in container.left (for example), which turns into container.right when switching to RTL, a problem that I wanted to avoid.

[widmoser]

@SomeKittens: I've added tests for RTL layout. From my side the PR is ready.

[asaf050]

Hey,
Any updates for this one?

Thanks