Make set location of the bootstrap library more easily modified.

The recent change with the implementation of allowing a bootstrap CDN is all fine and good, but I do not think it is wise to put the "else" statement of using the manually downloaded bootstrap library in the theme folder to be hard-coded in theme.inc.

The .info file is where where people assume that css and js files are added by default, and rightfully so. More advanced users may want to change how these files are included (placing the library outside of theme folder, using LESS files instead, etc.) and hard-coding the "default" method of including these files within theme.inc I think is not the best practice, as you have to search for how the files are even being included in the first place. Can we instead have the CDN "else" statement in theme.inc simply refer back to the locations set in the .info?