ImportSongs: Add Google Drive support

- Adds a new page for importing custom songs, where it is possible to pick a local folder (desktop only) or a Google Drive folder (desktop and Android)
  - This feature is disabled on iOS due to the lack of OGG audio support in the browser
- In order to not get rate limited, a TJA file is parsed for metadata only when the song is clicked in the song selection, rather than all at once at import time
- The instance maintainer will need to provide the API credentials in the config.py file to enable this feature
  - This requires a new project to be created at console.cloud.google.com
  - Drive API will have to be enabled
  - API and OAuth keys should be created
    - API key can be restricted to only have Google Drive and Google Picker APIs
    - OAuth Client ID should have Web Application type and JavaScript origins set
    - Editing the OAuth consent screen to have a name and icon is recommended
      - It is semi-required to submit the consent screen for verification as the permission to download all of the Drive files will be asked.
      - Note that the email of the maintainer is publicly visible on the consent screen
  - The project number can be found in the IAM & Admin settings page

public/src/js/controller.js

@@ -246,23 +246,15 @@ class Controller{
 					var songObj = assets.songs.find(song => song.id === this.selectedSong.folder)
 					var promises = []
 					if(songObj.chart && songObj.chart !== "blank"){
-						var reader = new FileReader()
-						promises.push(pageEvents.load(reader).then(event => {
-							this.songData = event.target.result.replace(/\0/g, "").split("\n")
+						promises.push(songObj.chart.read(this.selectedSong.type === "tja" ? "sjis" : undefined).then(data => {
+							this.songData = data.replace(/\0/g, "").split("\n")
 							return Promise.resolve()
 						}))
-						if(this.selectedSong.type === "tja"){
-							reader.readAsText(songObj.chart, "sjis")
-						}else{
-							reader.readAsText(songObj.chart)
-						}
 					}
 					if(songObj.lyricsFile){
-						var reader = new FileReader()
-						promises.push(pageEvents.load(reader).then(event => {
+						promises.push(songObj.lyricsFile.read().then(event => {
 							songObj.lyricsData = event.target.result
-						}, () => Promise.resolve()), songObj.lyricsFile.webkitRelativePath)
-						reader.readAsText(songObj.lyricsFile)
+						}, () => Promise.resolve()), songObj.lyricsFile.path)
 					}
 					Promise.all(promises).then(resolve)
 				}