Merge pull request #86 from aitjcize/api-name

Update toxcore API name.
Updated Travis to use Qt 5.2.0
Use system's default config file location for storing settings
Replaced native separators with nix separators when interacting with Qt

QDir::separator(), aka system native separator, should be used only when
displaying paths to a user. Qt internally expects '/' as a separator. More in
QDir::separator() doc.
Updated build instructions and build process to use Qt 5.2.0
Updated general information and build instructions
Replace placeholder implementation by Qt5.2 placeholder. Fix issue 76.
Merge pull request #89 from Schlumpf/qt52-placeholder

Replace placeholder implementation by Qt5.2 placeholder.
Made undo/redo disablable/enablable
Added a clear button to the filter widget
Fixed a bug of Esc not cancelling name/status changes
Made username and status message labels copyable
Moved some of context menus to stack
Removed unused variable, made some formatting fixes
Updated build instructions
Implemntation file receiving function.