Summarize by type, Initial type clean

Add summary by event type for analysis purposes.

Add cleaning of event types for obvious cases such as the various way
Tornadoes event types are worded.

Added function to return the biggest n instances located in a column of
a data frame. Use this to generate top event types for each category.
Can be used to select top individual events if passed larger data frame.
Add thoughts on what to discuss

Placed bullet points on possible areas to discuss in write-up.