Re-add shares archive table for 24h hashrates

This should fix #312 and fix #256 where hashrates are reset on quick rounds.
Users are not able to properly view their past 24h hashrates.

Will be merged once confirmed working.
Fixing PHP Warning on admin->user panel

This fixes #383
fixing stmt issue
Fixing pool hashrate graph

Should fix #312 completely.
Merge pull request #390 from TheSerapher/issue-383

Fixing PHP Warning on admin->user panel
Hard coded block limit for pool statistics

This should fix a potential DoS like attack when fetching a random
amount of blocks continously.

Fixes #387
Merge pull request #391 from TheSerapher/issue-387

Hard coded block limit for pool statistics
Enforce unique account emails

* display an error if user tries to re-use an email address
* moved SQL files to indicate the order of SQL import
* added unique email index SQL file

This will address #389, still needs email validation.
Fixing PHP warning message for empty price var

Fixes #375
More descriptive error message exceeding LTC threshold

Fixes #388
Fixing issue with delayed inserts for shares

When shares are inserted with a delay for performance optimizations,
this will cause block timestamps to be completely off with share
timestamps. Hence the timestamp limited search is now removed, it would
cause too many issues for Stratum users/pools.

Addresses #392
Merge pull request #393 from TheSerapher/issue-392

Fixing issue with delayed inserts for shares
Abort payout process if `share_id` is missing

If we have a block with NO `share_id` we abort the entire process. Less
of an issue with proportional since PPS is still being paid out, but a
block round will never actually end.

This will allow for manual intervention by the user. Otherwise blocks
found after the one having issues might trigger the payout process and
pay out shares of the old block in a more recently found one.

Please use #392 for further help on this, I have yet to replicate the
unknown block finder issue with the proper amount of upstream shares.
Merge pull request #394 from TheSerapher/issue-392-abort-payout

Abort payout process if `share_id` is missing
User proper archive table for union

Addresses #312
Merge pull request #395 from TheSerapher/issue-389

Enforce unique account emails

Fixes #389
Merge pull request #396 from TheSerapher/issue-375

Fixing PHP warning message for empty price var
Merge pull request #397 from TheSerapher/issue-388

More descriptive error message exceeding LTC threshold
Revert "Fixing issue with delayed inserts for shares"

This reverts commit 752b3e810fa9687e964122d602d2291123b3640a.
Merge pull request #398 from TheSerapher/issue-312-24h-hashrates

Issue 312 24h hashrates