Add licenses to Camel's top-level pom file.

Camel's top-level pom file is missing a licenses section. According to ScanCode, the following licenses are used by various components of Camel:

• Apache 2.0
• MIT License (camel schematron xsl & tooling/camel-manual css)
• BSD-Modified (camel-salesforce-component & camel-smpp)
• Academic Free License [AFL] >= 2.1 (camel-cometd tests dojo javascript)
• W3C-SOFTWARE-19980720 (components/camel-soap/src/main/resources/soap.xsd)

All these licences should be added to the top-level pom to allow automatic generation of product license files.