Fixes #325 geo facet polygon now removed when clear all clicked

Have linked the clear all link to the geo facet to clear the polygon and collapse the facet.
Code had two different return types

IMHO it is better to return undefined than an false which is different from the object
being returned in the opposite case.
Replaced tabs with spaces.
DRY up some of the filter creation code

Use a factory to create filter instances, they probably no longer need to be referred to
by name now either.
Merge pull request #386 from aodn/issue-325

Fixes #325 geo facet polygon now removed when clear all clicked