Save and modify functionality

[Terotrous]

This implements the ability to modify and save IPF files so you can change things in the client. It still needs a little bit more work to be a fully fledged editor but it's getting there.

[exectails]

Thanks for the PR. Could you quickly summarize what the current features are that you added? I think I recall you mentioning that creating new IPF files from scratch isn't working yet, is that correct? Also, I'd appreciate it if you could go over the code once more and adjust it to match the project's general coding conventions, such as using tabs for indentation, using PascalCase for public fields, etc.

[Terotrous]

• You can edit IES files and plain text files using the preview window
• You can save your changes to an IPF file
• You can drag-drop a new file into an IES file
• You can delete files or folders
• You can edit the version by clicking on it in the bottom left
• You can insert a row into an IPF file by right clicking the row indicator above where you want to insert

The interface could definitely use a bit of cleanup, and yeah, making a new file from scatch should be an option, but I've been using it a fair bit for my skill PRs (to give myself the removed skills).