Added concatMapStringsSep and concatImapStringsSep

Example: configure rewrite rules for Mediawiki

    RewriteEngine On
    RewriteCond %{DOCUMENT_ROOT}%{REQUEST_URI} !-f
    RewriteCond %{DOCUMENT_ROOT}%{REQUEST_URI} !-d
    ${concatMapStringsSep "\n" (u: "RewriteCond %{REQUEST_URI} !^${u.urlPath}") serverInfo.serverConfig.servedDirs}
    RewriteRule ${if config.enableUploads
Fixed rewrite rules for Mediawiki

If Mediawiki was served from the root directory of the server
it was impossible to serve other directories.

Make sure that URLs defined in servedDirs are not rewritten.
Use case: serving local copy of MathJax
Merge pull request #3780 from ip1981/master

Fixed rewrite rules for Mediawiki