include copies of all license files for dependencies

[kiniry]

I like the Apache Foundation's common practice of having them all collected in a subdirectory at the root of the project.

E.g., from their LDAP API:

/Users/kiniry/Sandboxes/LDAP/apache-ldap-api-1.0.0-bin
Free--Fair-2:apache-ldap-api-1.0.0-bin> ls licenses/
antlr-LICENSE.txt			xml-apis-LICENSE.dom-documentation.txt	xml-apis-README.sax.txt
dom4j-LICENSE.txt			xml-apis-LICENSE.dom-software.txt	xml-apis-README.txt
jbcrypt-LICENSE.txt			xml-apis-LICENSE.sax.txt		xpp3-LICENSE.txt
slf4j-LICENSE.txt			xml-apis-README.dom.txt```