Bug 19784: Adapt /v1/patrons to new naming guidelines

Bug 19784: Adapt /v1/patrons to new naming guidelines

This patch introduces two functions to the patrons endpoint:
- _to_api
- _to_model

This are in charge of field mappings in order to comply with the
guidelines.

Koha::REST::V1:Auth is adjusted to handle 'patron_id' as well. 'borrowernumber'
handling is kept until the existing endpoints get updated.

To test:
- Apply the patches
- Run:
  $ kshell
 k$ prove t/db_dependent/api/v1/*.t
=> SUCCESS: Tests pass!
- Sign off :-D

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>