Remove Unnecessary Code from Model Class

Remove Unnecessary Code from Model Class

`Model::__construct()` does not actually accomplish anything anymore. It
is just a stub to `ADOdb_Active_Record`

- Pass onto parent class by removing stub constructor
Fire group events in `UserInfo::updateGroups()`

Fire on_user_enter_group and on_user_exit_group in
`UserInfo::updateGroups()`

`UserInfo::updateGroups()` does not call `User::exitGroup()` and
`User::enterGroup()` and instead used single SQL `DELETE`.

- Fire group events for each group removed or added
Fix Tags Block Save in Stacks Dashboard Page

Fix tags blocks save in stacks dashboard page.

Block does not save propertly when in stacks dashboard page as blocks
are unable to save to the page based on `$_REQUEST['cID']` as they are
expecting to be in a page not a dashboard dialog.

- Check for being in the Stack Dashboard page and display accordingly
- Do not show tag attribute form in add / edit in dashboard page
Show errors in install script
Don't check for redirect if C5_ENVIRONMENT_ONLY

When C5_ENVIRONMENT_ONLY is set to true, the concrete5 should sanitize the
current URL.
Merge pull request #1558 from mlocati/avoid-redirect-check-when-c5_environment_only

Don't check for redirect if C5_ENVIRONMENT_ONLY
Merge pull request #1535 from mkly/fix_tag_block_save_stacks_dashboard

Fix Tags Block Save in Stacks Dashboard Page
Merge pull request #1534 from mkly/fire_group_events_userinfo_update_groups

Fire group events in `UserInfo::updateGroups()`
Merge pull request #1530 from mkly/cleanup_model_class

Remove Unnecessary Code from Model Class
Merge pull request #1557 from worldskills/error_reporting

Show errors in install script