context: introduce RequestContextMapper interface

and adjust the world to use it

Signed-off-by: Alejandro Mery <amery@geeks.cl>
middleware: add RemoveTrailingSlash()

Signed-off-by: Alejandro Mery <amery@geeks.cl>
dispatcher: Add GetStringArgument() helper

Signed-off-by: Alejandro Mery <amery@geeks.cl>
middleware: replace Bridge dispatcher with ScriptName middleware

Signed-off-by: Alejandro Mery <amery@geeks.cl>