Details
Description
As described in CRM-21260, CiviMail compose UI very slow to initialize when many mailing groups, past mailings and templates. The biggest factor was found to be the number of enabled message templates. See test results at PR 11142.
The proposal here is to switch to loading message templates on demand. I.e. do for message templates what CRM-20521 / PR 10303 did for the list of groups and mailings.