Small cahnges needed to make things work with QT5.
urlstr is alredy of type QString
Canceling download process cleanly (with SIGINT!) (fixes #14) and resuming download by default in Linux (fixes #15). Moved some todo tags into issue tracker.
Enable drag&drop of URL's into video list (fixes #18)
Refactored VideoTableModel usage hassle from MainWindow into model class
Added proper download canceling on quit
Added saving and restoring session feature. Fixes #19.

Tested in Linux only.
Fixed single command line download to not restore/save session

Related to #19
Added file name tooltip to videos

Very simple solution for issue #20
Fixed a typo in desktop file
Removed a stray column, set fixed width of columns
Enabled editing not yet started URLs during download.
Fixed removing videos during download
Fixed a couple of unused variables in MainWindow.cpp
Added installation tips for Linux to README.md, and fixed some typos in it
Merged Huulivoide's qt5 branch so that both Qt4 and Qt5 work

Warning: only testing presence of Qt5, so Qt6 won't work.
Added make install target for Linux
Edited README.md for installation instructions in Linux