URI Encoding the mailto links for 'sharing'

Adding a call to encodeURI to encode the urls used to generate
the mailto links, and the mailto links themselves. If this is
not done, then the urls can be corrupted if they contain any
reserved characters. This was seen in 18F/midas-open-opportunities#37,
which contained the identifier '20%'.
Merge pull request #398 from DavidEBest/devel-uriencode

URI Encoding the mailto links for 'sharing'