modules with mnesia and odbc backends unifications

[michalwski]

All modules storing data in mnesia or odbc have two version now (named with _odbc suffix or without). The common logic of these modules should be left in the original module and all backend related operations like read/write/update should be moved to some backend modules. Good example of similar solution are session backends (mnesia and redis).

Candidates for such a unification:

• mod_private(_odbc)
• mod_vcard(_odbc)
• mod_roster(_odbc)
• mod_offline(_odbc)
• mod_last(_odbc)
• mod_privacy(_odbc)

[arcusfelis]

mod_private(_odbc) is too small for this.

[michalwski]

I know it's small but is that a reason not to unify the logic and keep it duplicated?

[arcusfelis]

PRs for:

• mod_private Unified mod_private and mod_private_odbc #140
• mod_privacy Unified mod_privacy and mod_privacy_odbc #141

[michalwski]

mod_vcard is done in #142
mod_offline is done in #149
mod_last is done in #281

The last piece is mod_roster #139 which is still waiting for rebase.