W3C Validation, select elements, version_history.md

Fixed most if not all W3C Validation errors, as suggested in https://github.com/HackThis/hackthis.co.uk/issues/61

I also fixed an issue related to the unreadable text on the setting page's DOB visibility select element's options. (Happened to come across this on Chrome under Win8.1 just now) This fix should apply to any other select elements on the site that were previously unreadable due to the same issue.
Before:
![before fix](https://f.cloud.github.com/assets/3200580/2283272/f1e808c4-9fba-11e3-9cbe-18df9310f094.png) 
After:
![after fix](https://f.cloud.github.com/assets/3200580/2283279/087ddd20-9fbb-11e3-81e2-4f70513f4b17.png)