That's what the README suggests and - more importantly - the cmake
config file works with.
Also use angle brackets instead of quotation marks in two cases.

Allowing to build against a system installed copy.

This will cause the http::Client to not block & exit immediately
when we're calling Client::close

Signed-off-by: Vitaly Zaitsev <vitaly@easycoding.org>

- Remove the one time key that is used to create an inbound OlmSession.

Add a temporary fix for travis-ci with regard to wrongly exported include directories.