Improve project importing and event page

[Zegeri]

• I propose dropping support for Qt4 builds. In fact, the current editor won't compile with Qt4 since 2014 because we use some Qt5-only modules like QMediaPlayer (884da67).
• The commands of the event page should look now more familiar to the usual RPG Maker user.

This is how it currently looks like this. There are still some missing commands related to battle and the commands introduced by RPG2k3 1.11.

• To fix the issue of XYZ images of existing RPG Maker projects, we have two options, add support for XYZ reading on the go or convert them once when importing files. I've decided to go the latter way because it's much easier. Full XYZ support could be added in the future.
  
• Not many RPG Maker users will be interested in the line number of some event command, but it's useful for EasyRPG Player developpers to debug some games.
  

[Zegeri]

I found some issues, please, don't merge yet.

[Ghabry]

Awesome, 100 👍 for you. I have a reason now to revive the Editor (PR) builder for Windows :D.

The Windows project part is horribly outdated and will never compile this way. Will also open a PR later to fix this.

[Zegeri]

Issues resolved and rebased to the upstream HEAD.

[Ghabry]

Teleport parses wrong

[MarianoGnu]

Great work, but i want to know, what file is the "Line: 441" tooltip refered to?

[Zegeri]

It's its index in the list of command of the current event page. I added it for debugging purposes.