Improve meson build system + Make app translatable

[NathanBnm]

I made a few improvements to your app structure. These are not breaking changes. Let me know if you have any questions 😄

Changelog:

• Added .editorconfig file with elementary recommended config
• Deleted COPYING as long as there is already a LICENSE file
• Removed some deprecated configuration options
• Improved meson.build files
• Added some comments to meson.build files
• Improved and simplified post_install.py script
• Made the app translatable

I would be happy to add French translation once this will have been reviewed

[jhaygood86]

This is a very big PR, can you split it up into multiple smaller PRs for each individual change?

I'm not inclined to take the meson changes. Also, I already had a local branch that did translations, I just pushed that up.

[NathanBnm]

I'll split the changes in multiple PR if that's you want.

Regarding the build changes they create uniformity within the ecosystem of elementary apps which makes the code easier to read and maintain for contributors. These are not breaking changes.

Just checked the way you're handling translation. It's better to split the metadata translations from the main ones for clarity too.