Add a very basic logger for arethusa

This duplicates the console.log behaviour. We will still use this for
debugging purposes, but for logs we want others to see too we will use
the arethusaLogger. Jshint won't complain then - and we can still let
it track any forgotten console log statements.
Minor fixes in .jshintrc
Add arethusaLogger to jshintrc
Remove jshint arethusaUtil global declarations

We define it in our .jshintrc now.
Fix jshintrc

We cannot set the arethusa variables to read-only as we need to define
them for the first time at some point...
Merge pull request #59 from latin-language-toolkit/arethusa_logger

Arethusa logger