Misc changes and modifications

Gruntfile.js - Updated .htaccess download location.
.htaccess - Updated to latest version.
404.html - Updated default wording.
_mixins.scss - Updated mixins with oldie support that can be toggled on or off and other minor updates.
_variables.scss - Minor updates.
_base.scss - Minor updates.
_config.yml - Minor updates.
default.html - Removed IE conditional html tags, updated Google Analytics code, and oter minor updates.