Web IDE performance improvements

Over time in the Web IDE we have added more data into the Vuex store, most of the data doesn't get used. We should do an audit on the data & remove the data that is no longer required.

We also need to figure out the hanging when receiving the file list. For this we pass the data into a web worker to put into the format that we require, however when the data comes back Vue makes it reactive which then makes the browser hang (the more files, the larger the hang). I'm not really sure what we can do here, but its worth investigating as its noticeable especially with GitLab CE.