Improve NDEF API's

o Add NdefRecord.toMimeType()
  Maps the record to a MIME type
o Add NdefRecord.toUri()
  Maps the record to a URI
o Add hidden NfcAdapter.dispatch()
  Helps test the dispatch path.
o Modify createMime(), createUri() and createExternal():
  Do not try and strictly follow RFC requirements for URI or MIME content
  types. This just leads to heartbreak - the RFC requirements are too strict.
  For example RFC1341 forbids the use of '.' in a MIME type, however this is in
  common use in types such as "application/vnd.companyname". I think the best
  approach is to only remove 'obvious' whitespace issues, and to convert
  uppercase to lowercase as per Android guidelines.

Change-Id: Id686f5f3b05b2dceafad48e1cfcbdb2b3890b854