Date fields in all popups should display calendar icon

In several CiviHR extensions (hrqual, hrcareer, etc), we create a tab based on a profile form. When a user clicks "Add new record" or "Edit" in the form, a popup appears. Inside that popup, date fields do not appear correctly – i.e. the calendar icon does not appear next to them.

One theory (untested for this particular bug) – Popups often suffer from styling issues because of how the CSS rules are targeted. For a long time, all Civi's CSS rules were written to target "#crm-container". However, as we started introducing more AJAX UIs, it became harder to put all our content within one "#crm-container" DIV – e.g. popups often add new top-level DIVs. Consequently, we started introducing DIVs with class="crm-container" and updating our CSS rules to work with either. There could be some mismatch. (Note that we have not switched wholesale or removed #crm-container rules. The #crm-container rules give higher precedence which helps in cases where the CSS from CMS+Civi conflict.)