Add LargeNumber Formatter.

Formats large numbers to short strings. Ex:

1000000 --> "1.00M"
1234567890 --> "1.23G"

Close #577.
Change name to SISuffix Formatter.

Since that's what it does. It also shortens small numbers, so
there's a test for that too.
Add in SISuffixFormatter.ts
Merge branch 'master' into 577-large-number-formatter
Merge pull request #595 from palantir/577-large-number-formatter

Add SISuffix Formatter.