Catch error results from execute() and don't implode on non-arrays.

Needs proper error handling
add lowlevel check for existence of writable extensions directory
Merge pull request #1564 from GawainLynch/hotfix/CommandRunner-implodes

Catch error results from execute() and don't implode on non-arrays.
Merge pull request #1567 from jadwigo/master

proposed fix for https://github.com/bolt/bolt/issues/1512
Merge pull request #1568 from rossriley/extensions-lowlevel-check

Add lowlevel check for existence of writable extensions directory
do not isolate $app
update js and css snippets to point to new extensions paths
fix bug
remove extra slash
add new getBaseUrl method to calculate relative url
Dirty fix for 'event is not defined' clicking _backend/user_
Clean solution for missing global event obj in FF
Working on #1377
Merge branch 'master' of github.com:bolt/bolt
Merge pull request #1572 from rixbeck/issue-1571

Do not isolate $app on bootstrapping
Merge pull request #1573 from rossriley/extensions-improvements-fixes

update js and css snippets to point to new extensions paths
Merge pull request #1574 from rixbeck/issue-1563

Dirty fix for 'event is not defined' clicking _backend/user_
Moving the 'messages' below the main headline.