HaikuDepot: Refactor of Login

These changes cover a rework of the login and
account creation logic before making additional
changes related to the user usage conditions.

Relates to #15209

Change-Id: I90b7dbcee5b0285476938c6ced0afc89483d6227
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2023
Reviewed-by: Stephan Aßmus <superstippi@gmx.de>
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: 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>