Added 8 digit estimates precision and balance

This expands the prevision for LTC estimates to 8 digits. Since the
sidebar was widened, they should fit for most resolutions.
Merge pull request #364 from TheSerapher/round-estimates-precision

Added 8 digit estimates precision and balance
Adding input check for AP and Donation

Fixes #354
Merge pull request #365 from TheSerapher/issue-354

Adding input check for AP and Donation
Properly allow '0' as a workername or password

This fixes #347 as recommended at

http://de3.php.net/manual/en/function.empty.php

We allow anything else than an empty string.
Merge pull request #366 from TheSerapher/issue-347

Properly allow '0' as a workername or password
Do not return null on empty valid/invalid shares
Link API key to User API Call

Fixes #367
Removed var_dump debug output
Merge pull request #368 from TheSerapher/issue-367

Issue 367
Adding further IFNULL checks to statistics class
Changed error catching in pools page
Adding link to JSON API to server stats page
Adding getpoolstatus API Method

Fixes #369
Merge pull request #370 from TheSerapher/issue-369

Issue 369
catch PHP warning
allow empty blockexplorer URL
updated dist config
Merge pull request #373 from TheSerapher/issue-372

Issue 372
remove link to block when blockexplorer empty