Add Tumblr icon with SVG and Fallback Character

- Add Tumblr icon.
- Add Tumblr SVG.
- Add Tumblr Fallback Character. *( http://codepoints.net/U+1D565 found using http://shapecatcher.com )*
- Update Changelog.
- Update bower.json.
- Update fontcustom-manifest.json.
- Built with Grunt.


![tumblr_icongs](https://cloud.githubusercontent.com/assets/1189414/5048022/6fed3c34-6bf9-11e4-930d-4637e154792a.jpg)


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