Remove empty element after trimming them

This makes sure we do not accidently keeps empty element into the
recipients array.
Make sure numeric keys works

Right now, if you pass a non-keyed array as a recipients value, it does
not works. The empty calls returns true on the 0 key (index) and false
otherwise. This mixes up sendmail and make the delivery
non-deterministic.

I've replaced the empty calls with intval: this way, the can properly
distiguish key based and non-key based array.
Use consistent logical operators favouring those with higher precedence
Remove unused code and comments, clean up static references
Update autoloader with missing classes
Make the Select Box extend the Tag List field, they share very similar code
Remove parenthesises from query

Fixes #2279
Removed sections index from options for default area for managers
Method getFilterQuery has one argument only
Merge branch 'integration' of https://github.com/jensscherbl/symphony-2 into integration
Merge pull request #2286 from jensscherbl/integration

Removed sections index from options for default area for managers
Make checkbox field able to process boolean values.
Merge pull request #2278 from DeuxHuitHuit/multiple-rec

EmailGateway: Multiple recipients problem with sendmail when using non-keyed arrays
Minor PHPDoc fixes
Simplify Symphony's isLoggedIn and initialiseDatabase functions