Custom ticket numbering format

Ticket numbers are now configurable as a system-default and by help topic. Previously, an administrator could select between six-digit random and sequential numbers. Now, the sequence is selectable so multiple sequences as needed, and a format can be specified to define how the ticket numbers look. Formats can also be defined for each help topic.

![screen shot 2014-07-29 at 8 46 16 am](https://cloud.githubusercontent.com/assets/672074/3735683/e4f13026-1726-11e4-99b2-e95bf53138cd.png)
Tickets have configurable ticket numbers

![screen shot 2014-07-29 at 8 46 32 am](https://cloud.githubusercontent.com/assets/672074/3735691/fa773ecc-1726-11e4-8306-f09caa63ff87.png)
Configuration for default system ticket numbering format

![screen shot 2014-07-29 at 8 46 40 am](https://cloud.githubusercontent.com/assets/672074/3735698/05ab3b72-1727-11e4-9271-3290ff9567f4.png)
Configure a sequence for ticket numbers

![screen shot 2014-07-29 at 8 46 56 am](https://cloud.githubusercontent.com/assets/672074/3735701/1251e9fc-1727-11e4-9fcc-cddb727b80eb.png)
Add or edit a sequence — set padding, increment, next value, and the name

![screen shot 2014-07-29 at 8 47 16 am](https://cloud.githubusercontent.com/assets/672074/3735707/2430d700-1727-11e4-85de-f79d68dbe66c.png)
Configure ticket number formats for each help topic (optionally)

Should we add a validation error for number formats without a single `#`?