travis: Switch to Qt 5.2
Require Qt 5.2 when building for Qt5

QUrl got a couple of fixes [1] [2] in the 5.2 release. Without these changes,
the mailto: parsing is broken -- see [3] for details on what exactly fails. As
such, building with Qt 5.1 is no longer supported.

[1] https://codereview.qt-project.org/#change,60266
[2] https://codereview.qt-project.org/#change,60267
[3] http://git.reviewboard.kde.org/r/112767/#review44852
Add support for RFC 6068 mailto: URL schemes

Test examples from the RFC are also added to the unit tests.

v2: jkt: Fix coding style, remove build failure in the unit tests, don't call
QList::reserve as that isn't available in Qt 4.6 which we still support and fix
the Qt5 build.

REVIEW: 112767
Coding style

Removal of extra spaces and adding curly braces where they IMHO make sense.