Faster search, faster startup, 160MB less memory usage

-Package search up to 50% faster (on top of last performance patch #23 )
-Memory usage reduced by 160MB
 --Removed overhead on package and review classes
 --Changed search caching from patch #23 after profiling showed some parts were unnecessary
-Mintinstall startup time reduced from 8380ms to 5200ms (in test VM)
-Bug fix, search occurs twice after pressing enter due to 'search while typing' callback
-'search while typing' timeout changed from 1000ms to 400ms, as the quick searches don't affect user's typing anymore.
Merge pull request #34 from LukePH/speedup2

Faster search, faster startup, 160MB less memory usage