Allow IO manipulators for pion::http::writer

Overload the write() method and the stream operators
for iomanip functions like std::endl.
Hide common "Lost connection" message

This just happens regularly during normal operation.
Let's keep the log clean of such messages.
Register webfont MIME types

This silences the browsers' error consoles a bit.
Merge branch 'common-errors' of https://github.com/hasselmm/pion into develop
Merge branch 'webfonts' of https://github.com/hasselmm/pion into develop