Create ApplicationController::Filter#process_datetime_selector

Code deduplication (DRY)
Create ApplicationController::Filter#process_datetime_selector

Simplified character extraction from a string.
Create ApplicationController::Filter#process_datetime_selector

Explicitly declare this new method as private.
Create ApplicationController::Filter#process_datetime_selector

Simplified boolean logic around time_suffix computation.
Create ApplicationController::Filter#process_datetime_selector

Use new variable exp in place of @edit[@expkey]
Create ApplicationController::Filter#process_datetime_selector

Computed exp_value_key and defaulted exp_key to nil.
Create ApplicationController::Filter#process_datetime_selector

Compute value_key, instead of passing it as parameter.
Simplified ApplicationController::Filter#process_datetime_selector method
Fix error display w/o session.

Fix display of errors w/o a valid session by:
  * wrapping @css[:background_color] into css_background_color,
  * adding rescue to role_allows.
Fix: session[:last_trans_time] was not set.

session[:last_trans_time] is not set in the login request but later.
We need to anticipate this in the PrivilegeCheckerService.
Add tests for referer checking on requests.
Refactor and cleanup validate_user in DashboardController.
Simplify set_user_time_zone.
Simplify ie8_safe_redirect calls.
RBAC: refactor and remove fallback.
Fix small issues in English locales.

Remove spaces at the end of line.
Fix one key.
Fix a typo.
validate_user: fixes and tests.
Fix specs according to Rubocop complaints and review comments.
Fix specs after RBAC refactoring.
ApplicationController: better name for a method.