renames isAdmin? to is_admin? in User model
adds a view to set testbedcredentials to users
adds a big red warning if user has no testbed
fixes insecure deletion of users
removed obsolet comment
add delete dependency to user testbed credetials
changes default database to MySQL

SQLite had major problems with concurrent transactions which occur
often when an experiment is run. The job worker and the rails server
are on two different threads.
modifies seeds.rb to actually seed the new db
adds a select-tag for testbeds for new runs

this closes #1