Potential fix for PHP Warning

This should fix #327
Fixing PHP Warnings in Registration page

* Fix API Key generation not using SALT when creating hash
 * This should not affect existing API keys since hashes are compared
* Fix PHP Warning for RECAPTCHA if disabled

Fixes #328
Merge pull request #333 from TheSerapher/issue-328

Fixing PHP Warnings in Registration page
Merge pull request #334 from TheSerapher/issue-327

Potential fix for PHP Warning
Show nethash rate in MHash/s not GHash/s

* Easier to compare directly with pool hashrate
* Better display format for low nethash rate coins

Fixes #331
Merge pull request #335 from TheSerapher/issue-331

Show nethash rate in MHash/s not GHash/s
Merge pull request #1 from TheSerapher/next

Next