MDL-41437 rework plugin_manager caching and version info in blocks and modules

This patch includes:

* version column removed from modules table, now using standard config, this allows decimal version for modules
* version column removed from block table, now using standard config, this allows decimal version for blocks
* module version.php can safely use $plugins instead of module
* new plugin_manager bulk caching, this should help with MUC performance when logged in as admin
* all missing plugins are now in plugin overview (previously only blocks and modules)
* simplified code and improved coding style
* fixed pluginlib unit tests