Support for FMX, checking multiplatform

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Add support for FMX (it's very,very,very painful!)
Check compatibility with other platforms

Any test results from specific platforms (Mac OS, kali linu... khm ubuntu 16) will help

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With gtk it works quite unpredictable, the message context is very specific to an action, which message is sent to be done.
Unlike windows, it handles arrow keys only when Properties panel is hidden, and it's caused by handling key/char messages by text controls. I don't know exactly how to solve that problem, but, i think, i can repair that malfunction just by adding WM_CHAR case to the list of clauses.
Also, it has several problems with transparent topmost forms, which cannot support both semitransparency and opaque style at the same time.
The next question is how to make it run smoothly on every supported (now - partially) OS.
[I think, the custom drawing is the key]

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I made it to work smoothly, however, Lazarus doesn't support shaped forms on GTK-2, so, i need to add some conditional, but which exactly?

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I've updated conditionals, thanks to Zelijko