Added "system"->system_error_email to Settings

E-mail address for system error notifications
Changed email address to new "system_error_email" setting on PPLNS Cron
Changed email address to new "system_error_email" setting on Prop Cron
[FIX] Exclude invalid shares from statistics

* Hashrates
* Sharetes
* Time Graphs

Fixes #797
Merge pull request #800 from nicoschtein/patch-4

Issue 799
[FIX] Honor custom HTTP ports

Fixes #803
[FIX] Propagate dashboard when API disabled

Fixes #804
Merge pull request #806 from TheSerapher/issue-804

[FIX] Propagate dashboard when API disabled
Merge pull request #805 from TheSerapher/issue-803

[FIX] Honor custom HTTP ports
Merge pull request #798 from TheSerapher/issue-797

[FIX] Exclude invalid shares from statistics