Rename formfactor property to gwtp.formfactor to prevent conflicts

Commit f1c84c0 is a partial fix for [issue 401](https://github.com/ArcBees/GWTP/issues/401).  I don't think anyone will have a problem with it.

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Commit cdc370d is a fix for [issue 409](https://github.com/ArcBees/GWTP/issues/409).

It does formfactor detection based solely on user agent.

#### Advantages over the old system:

New code detects high dpi android phones correctly as mobile.

Windows computers with touch capability in metro mode get served tablet version.
Windows computers with touch capability in desktop mode get served desktop version.
Windows computers without touch get served desktop version.

All kindle devices get served tablet version.
The old code would serve desktop to kindles with silk enabled.

Blackberry tablets are served desktop version with old code.  Are detected correctly by new version.

#### Disadvantages:

Android tablets that include mobile in their user agent get the mobile version.  This should only affect first gen tablets that have not been updated.  I think it's better that a tablet get the mobile version than a phone get the tablet version.  Also I assume there are more S3 phones than all 1st gen tablets combined and the new code gets the formfactor right for that phone.