Added nomination searching.

Integrated logic from [my nomgrep plugin](https://github.com/CrimsonTautology/nomgrep).  Allows players to filter the nomination list by sub string.  For example typing `!nomsearch koth_` would generate a list of all koth maps on the server.  Or if you know you want to play koth_ashville, but are unsure of what version is on the server you can type `!nomsearch ash` to filter the menu by all maps containing "ash".  This is great for servers that have huge map lists and you don't want to press 9 a bunch of times to get to the map you want.