Arrow keys (and other keys that do not produce a character) sometimes do not work

[yonojoy]

Steps to reproduce

• Compile and start the demo applicaiton
• Click into the FMX edit field
• Enter a
• Press the tab key
• Press SHIFT+TAB to return to the edit (maybe the carret wont display because of issue #15)
• Enter c
• Press the left arrow key
• Enter b
• You will read acb but correct would be abc

The cause for this seems to be related to the focus handling. Normally the FMX form will get these key events, then everything is working fine. (For instance after clicking on the edit). But sometimes the FiremonkeyContainer will get these key events, then they are lost. (For instance after returning from another dialog).

[yonojoy]

I added pull request #14, that will fix most of the problem. However, I am not sure if it would be better a better fix to target the underlaying focus problem. One problem remains after the fix: ALT key seems to be handled differently. For instance ALT+arrow wont work - it does not trigger the event. Any idea?