[NEW] Customizable default directory view

[ohmonster]

Allow the user to set whether the Directory page initially displays the Channels list or the Users list.

(Related refinements: update style sheet so scroll bar appears with long lists when viewed in the Windows client. When changing tabs, set the sort values to be consistent with the initial directory display.)

Closes #12003

[CLAassistant]

All committers have signed the CLA.

[ohmonster]

This would close #12003

[mnlbox]

@ohmonster can you provide some screen shot?

[ohmonster]

@mnlbox Here is the new setting in administration.

One thing that became more noticeable when channels was no longer default was the default sort on the channels list. It was different depending on whether the list loaded by default or if you clicked Users then Channels. This PR makes the initial sort the same for both (by User count, descending)

[sampaiodiego]

Thank you for the contribution 😄

I had to do a small fix regarding our new lint rules, it's now fine to merge 🚀