[IMPROVED] Transaction data handling

This will improve loading times on large transaction tables. Thanks
@feeleep75 for helping with this one.

* Do not use SQL_CALC_NUM_ROWS since it will do a full table scan
* Allow admins to disable account transaction summaries to speed up page
  loads on large tables
* added new admin setting under system to Disable TX Summaries

Fixes #1065 once merged
Merge pull request #1077 from TheSerapher/issue-1065

[IMPROVED] Transaction data handling