add image sizes, default thumbnails to posts

REF: PR from @ericrasch - https://github.com/CMN/HomeInsurance.org/pull/3
oops, label it Images so it's easier to find
get pages by slugs

REF:
https://gist.github.com/germanny/9399616
https://gist.github.com/ericrasch/4723316
keep nomenclature consistent
add display_post_thumbnails function
remove invasive image setting
set up the default photo
changed preview-img to post-thumb to match what we're doing everywhere else
add function to display post thumbnails
Merge branch 'refs/heads/master' into generic-custom-functions
correct the default photo link
relinquish control of image's url
Merge branch 'master' into generic-custom-functions

Conflicts:
	app/templates/themes/genesis-child-theme/functions.php
	app/templates/themes/genesis-parent-theme/modules/mod-post-preview.php
Merge pull request #5 from jimmynotjim/generic-custom-functions

Generic custom functions