Web application / offline versions

Hello! Essentially, this update [re-]introduces ability to run Terrasavr offline.

First, you can install now install Terrasavr as a "progressive web app" - if you are using a compatible browser, a (+) button will appear in the address bar, and clicking it will make a local copy of the program, which you'll be able to access through the browser's Apps section - even if you are offline.
Currently this feature seems to be mostly supported in Chromium-based web browsers (Google Chrome, Microsoft Edge Beta, Opera, Brave, Yandex Browser, etc.)

Second, there is now a downloadable version offering more or less the same features - once you have ran it once (so that it can grab the needed files), it can be used offline indefinitely.

To note, these are fairly experimental, so there may be minor issues.