Resource cache size evict threshold improvements

* make the threshold configurable using a new Readium option
* in the absence of configuration option, try to determine the value
 based on browser's heap statistics before falling back to the default
 value of 100 MB.
Remove the implemented TODO comment.
Escape : namespace separator only for jQuery selector
Merge pull request #80 from readium/feature/resource-cache-configuration

Feature/resource cache configuration
Enable Readium to open File objects directly
Merge pull request #81 from TEA-ebook/dev/svg-image-blob-href-bug

Replace image href in SVG element with blob url
Merge branch 'develop' into tea
Merge branch 'dev/blob-zip-resource-fetcher' into tea