Support less (via dynamic config prioritization of dependencies)

Don't know if this pull request is welcome or not, because I changed some parts of `prioritizeDependencies` and I don't know If understand them completely ;)

I tried to add Less support to https://github.com/stephenplusplus/grunt-bower-install via
````
        fileTypes: {
          less: {
            block: /(([ \t]*)\/\/\s*bower:*(\S*))(\n|\r|.)*?(\/\/\s*endbower)/gi,
            detect: {
              css: /@import\s['"](.+)['"]/gi,
              less: /@import\s['"](.+)['"]/gi
            },
            replace: {
              css: '@import "{{filePath}}";',
              less: '@import "{{filePath}}";'
            }
          }
        },
````
but this didn't work as expected. It wasn't caught by `prioritizeDependencies` in `lib/detect-dependencies.js`, because these function doesn't use the `fileTypes` settings which are generated later at `lib/inject-dependencies.js`. So I moved some config stuff into `wiredep.js`(which fits quite well, because all other default configs are generated here, too). Now `prioritizeDependencies` calls every detect-able file types :)