This PR adds the ability to import field values into RangeEnabled frames
using the `pilosa import` command.
Example:
```
pilosa import -i i -f f --field foo sample-vals.csv
```
imports data from sample-vals.csv, which contains data in the format:
```
[ColumnID, Value]
```
Also fixes a bug where `frame.rangeEnabled` was not being set on frame creation.
This was populated by the `time_granularity` query argument, but that isn't being used either.
I believe this is left over from an early version of Pilosa prior to `Range()` query support.
this affects the scanner/parser and makes it produce signed ints rather than
uints, and so it affects all code that is expecting unsighed ints to come out of
the parser.
