Minor fixes for browsing off via file URLs (RELATIVE_URLS=True).

[rmorehead]

When using pelican-elegant with RELATIVE_URLS=True there are a few minor issues this corrects:

1. The bootstrap CSS won't load due to lacking http: at the start of the URL.
2. Home and site link take you to the directory, which just gives you a list of files if running directory off the filesystem.

[calfzhou]

I use RELATIVE_URLS=True, but didn't meet the given problem.

Your problem might be caused by that you directly open index.html in your browser. The correct way is to run python -m SimpleHTTPServer <port> in your output directory, and then visit your site from http://localhost:<port>/

[rmorehead]

I know it can be accessed via the stand alone web server, but with this minor change it works well for me running directly off the filesystem which is more efficient.

[calfzhou]

Add http: to bootstrap cdn might lead some problem if someone deploy his site using https.

[talha131]

I am closing this pull requests for all the reasons mentioned by @calfzhou.

Thank you @rmorehead and @calfzhou for your contribution.