HaikuDepot: Refactor usage conditions windows.

* Set only a minimum width and then resize to preferred on window.
* Set a minimum height for the text view itself.
* Use the new TextView controls instead of the old BTextView.
* Adjust other size constraints as needed.

Fixes #17998.

HaikuDepot: Error Reporting Improvement

When editing a user rating it can be that the user
is not authenticated properly or there is some
problem. This change improves the error reporting
in this situation to give the user a better idea
about what is going on.

Change-Id: Ib8890c2ea8a7316849486e472aabec05788243ef
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2112
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

HaikuDepot: Display User's Usage Conditions

A HaikuDepotServer may have previously agreed to
user usage conditions. If this is the case then
they are now able to view those conditions. There
were some problems with date formatting in this
change and so the date formatting logic has moved
into the HaikuDepot source code temporarily until
issues with the BDateTime class can be resolved;
most likely as a separate piece of work.

Relates to 15209

Change-Id: Ic3e5413d9139f410d7f7e8b566d4c56352dd2778
Reviewed-on: https://review.haiku-os.org/c/haiku/+/1870
Reviewed-by: Stephan Aßmus <superstippi@gmx.de>

HaikuDepot: Conditions on Create User

When the user chooses to create a new user they
are able to view the current usage conditions for
users. They are also required to agree to the
conditions and they are required to confirm that
they meet the minimum age requirement.

Relates to 15209

Change-Id: I83cdaabe1b3da31a4cd21139b72341f4b93cab85
Reviewed-on: https://review.haiku-os.org/c/haiku/+/1842
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>

HaikuDepot: Display User Usage Conditions

This change will allow the user to view the user
usage conditions from the HDS system in a
HaikuDepot window. The display of the text is not
currently well formatted in that the Markdown is
not yet properly parsed, but the display of the
data is working.

Relates to 15209

Change-Id: Ia6ad4ef995f5fe3c29c40221964e44d4554a033d
Reviewed-on: https://review.haiku-os.org/c/haiku/+/1750
Reviewed-by: waddlesplash <waddlesplash@gmail.com>