Style date time picker

[filwie]

Here are some style tweaks to datetime picker. Hopefully it will blend better into the whole UI.

Suggestions are welcome :) I am not so sure about border color. There is also distinct color for keyboard selection that might be a bit too different from mouse selection color - let me know what you think.

Here are some pictures:

Here we have date selected, date hovered with mouse pointer and date selected using keyboard all at the same time:

This should close #142 when finished

[bzurkowski]

@filwie I cannot see the new styling:

Can you check in your setup after rebasing with master?

[bzurkowski]

Managed to fix after subsequent rebuild.