#176003 by yched, KarenS, dvessel: put module installs into a batch, solving the following issues:

 - possible timeouts with installing/enabling lots of modules at once in core
 - enable install profiles to have more modules without fear of timeouts on install
 - bootstrap Drupal before each module load, so previously enabled modules are bootstrapped
 - let modules run their hook_requirements() (although actually calling them will be possibly fixed in another patch)