Further attempt to clean up transactions list

This hopefully cleans out remaining PHP warnings and table issues with
no/partial transactions available. Please test this out and report back
in #315.
(#376) Fix HTML/CSS markup at Statistics page
Merge pull request #379 from ilya-stromberg/issue-376

Fix #376 HTML/CSS markup at Statistics page
Use poolhash rate if nethash is smaller

This should avoid some confusion for coins where the network hashrate
drops under the pool hashrate due to slow block finding rates.

Fixes #378
Merge pull request #381 from TheSerapher/issue-378

Use poolhash rate if nethash is smaller
Fix PHP Warning on user login

While at it, I also extracted the hash function into it's own getHash
method. This will allow easy changes to hashing for string in the
future.

Fixes #382
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.
Change message on empty donor list

This fixes #380.
Fixing PHP Warning on admin->user panel

This fixes #383
Merge pull request #384 from TheSerapher/issue-315

Further attempt to clean up transactions list
fixing stmt issue
Merge pull request #385 from TheSerapher/issue-382

Fix PHP Warning on user login
Merge pull request #386 from TheSerapher/issue-380

Change message on empty donor list
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