Unified mod_offline and mod_offline_odbc

[arcusfelis]

Deleted unused functions:

• update_table()
• web admin callbacks

Resurrected mod_offline_odbc.There are 2 versions of it:

• mod_offline_odbc uses a new table, multiple row inserts and stores each field in a separate column. It also supports multiple hosts;
• mod_offline_odbc_legacy reproduces original behavior.

[michalwski]

This pull request adds odbc support mentioned in #87 (mod_offline_odbc)