Change operation_history to generic_index, #403

[abitmore]

For #403

[oxarbitrage]

getting error when starting node with changes:

...
2404818ms th_a       undo_database.hpp:68          ~session             ] 10 assert_exception: Assert Exception
maybe_found != nullptr: Unable to find Object
    {"id":"0.0.0"}
    th_a  index.hpp:111 get

    {}
    th_a  undo_database.cpp:123 undo
terminate called after throwing an instance of 'fc::assert_exception'
Aborted
root@NC-PH-1346-07:~/bitshares/pull464/bitshares-core# 

[abitmore]

Sorry for that. New commit pushed.

[oxarbitrage]

working now, nice work.

[abitmore]

Note: perhaps should bump db_version when releasing.

[abitmore]

Some data from live test: this change saves around 500M of RAM with current chain (head_block ~= 21614538) and default config(max-ops-per-account = 1000 and partial-operations = true).

[pmconrad]

Wow, I didn't expect that much!