Add a help panel and buttons to access it

Always available, slides in from the side (ish). Content
still a work in progress. Needs way to translate it.

For #92.
Display help the first time the app is run

Also record when help has been viewed so we don't display it again.

For #92.
Scroll help to top once dismissed

Not sure if this is the correct thing to do but having the help
re-appear scrolled to where you left it doesn't feel right.
Tweak help panel to work on Android 2

Android 2 doesn't support overflow: scroll so instead make the panel
full screen so you are scrolling what seems to be the screen. This means
we need to reset scrollTop before hiding it as otherwise the underlying
page is also scrolled.
move help content to a template

Rather than hard coding it into index.html. Loaded by the help init code
change help panel to overlay whole page

This prevents clicks on things 'behind' the help
improve post help show callback readability
remove debug output
Refactor first time help showing code to a method

For the reduction of duplicate code
Better name and even less duplicate code for first time help display
missing template file