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.