Changes

mnesia_db_euicc: renovate handling of euicc table (mnesia, REST)

The REST API that allows users to set certain eUICC parameters
(we call them "states" from now on) only allows to set eUICC
states, but doesn't allow to read them back.

With this patch, we renovate the handling of the mnesia euicc
table from the ground up so that REST API users have read and
write access to the states stored in the mnesia euicc table.

Related: SYS#8100

The original purpose of the euicc table was to hold static params
for an eUICC (e.g. the public key or the flag that tells if it is
a consumer eUICC or not). Now that we plan to extend the scope
of the euicc table, it makes more sense to talk about states rather
than parameters.

Change-Id: I74c602555b194a28d6eb9dd67ec4c6a8865fcb77