HTTP: Support POST method

[germanescobar]

The HTTP Processor should support POST method.

[germanescobar]

Done. The following configuration attributes were added or modified:

• method (String): GET or POST. Defaults to GET.
• encoding String): defaults to ISO-8859-1
• additionalParams (Map): a map of strings with additional query string.
• basicAuth (boolean): use basic authentication? Defaults to false.
• username (String): the username used for basic authentication. Required only if basicAuth is true.
• password (String): the password used for basic authentication. Required only if basicAuth is true.
• mapper (Map): changes the name of some attributes when building the query string.