Bug 20568: API keys management in interface

Bug 20568: API keys management in interface

This introduces the concept of API keys for use in the new REST API.
A key is a string of 32 alphanumerical characters (32 is purely
arbitrary, it can be changed easily).
A user can have multiple keys (unlimited at the moment)
Keys can be generated automatically, and then we have the possibility to
delete or revoke each one individually.

Test plan:
1/ Go to staff interface
2/ Go to a borrower page
3/ In toolbar, click on More -> Manage API keys
4/ Click on "Generate new key" multiple times, check that they are
   correctly displayed under the button, and they are active by default
5/ Revoke some keys, check that they are not active anymore
6/ Delete some keys, check that they disappear from table
7/ Go to opac interface, log in
8/ In your user account pages, you now have a new tab to the left "your
   API keys". Click on it.
9/ Repeat steps 4-6

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>