Adjust slider font.
Update foreBG panel to pen panel.
Update Android Studio.
Update pen button image to reflect selected colour.
Fix panel colour strange arengement.
Fix color picker flush bug.
Change button order because pen-color and rec button was too close.
Modify colour picker left position so that it align to pen button.
Ver 3.1
Fix icon garbage bug.
Stop tracking gradle-wrapper.properties (why tracked?).