Launch link is now constructed using functions for serializing JSON and assembling URLs

Addresses https://github.com/garemoko/moodle-mod_tincanlaunch/issues/2
replace logo with Tin Can logo
fixes some bugs introduced in 6ec949693e91e8fe135cd366f3b761868363b456
Add registration

Note: This commit breaks bookmarking (for now).
generate launch url at launch rather than putting it on the page
attempt to save and get a list of registrations from the state
stores and returns the registration id

This code is still not in a usable, production form but it's getting
there.
handles http error codes
Now stores multiple registrations

Next job: display the data nicely and allow for launching multiple
registrations
Added registration launch table
launch links per registration

yay!
identify user by email or fall back to account

Note: it seems very hard not to supply a user email in Moodle.
Update readme.md with instructions
add maturity and release info
Merge pull request #3 from garemoko/development

Handling of multiple attempts using registration