Fix missing enum case warnings
Fix a bug where the MainWindow cannot size properly on OS X

For some reason, Qt under OS X ALWAYS reports that the window changes
from maximized to normal state on the inintial resizing. This makes
the window on Macs have a faulty initial window size on launch.

Since this is not an issue on any other platforms, and the behavior
doesn't really make enough case to justify time looking for a general
solution, I'll just make this a special case. Since windows on OS X
doesn't have a "maximized state" anyway, we'll just ignore this
particular event on Macs.
Replace obsolete QProcess::setReadChannelMode
Add "Portable Mode" and change settings file storage

UJ::absoluteDataStoragePath now checks a file in the application
directory called "PORTABLE" (without the quotes). If the file
exists, Qelly enters "portable mode" and reads its config files
from the working directory. When the file does not present, Qelly
loads the config files normally from the users data storage path.

To make the config files' path structure consistent between both
modes, the main config file (qelly.ini) is now saved in the same
directory as sites.json and emoticons.json, instead of a seperate
system-dependant path. Users should move their existing config
files manually.

Fixes #44