Make the game playable on mobile devices

[Siriah]

Playing Codegarden in a mobile browser doesn't work properly yet. I had the following issues on my Android smartphone:

• The game is too large to fit in the Chrome window and can't be zoomed
• Drag/drop activates too quickly when trying to press a button
• Tooltips aren't as nice (they appear after tapping a button, which is not the ideal time to present such information)
• Double-tap can activate by accident when pressing a button twice in a row. The unwanted zoom can then not be cancelled except by double-tapping an HTML part of the GUI, because the Phaser canvas has its touch events turned off.