annogen Android fix missing EPUB controls on recent versions of Android that return non-null MIME type for xhtml

annogen Android apps: fix WebView crash on some 5.1 tablets (black screen shortly after startup) due to some JS injection not being on UI thread

annogen Android apps: fix for Android 4.3 and below crashing Back button bug introduced in v0.6594 May 2019

annogen Android apps fix NegativeArraySizeException reading epubs when an item's size is not stored in the zip record + bump targetSdkVersion as per Google Play requirement for November

annogen Android app: version stamp add version name when possible (for consistency with what's-new logs)

annogen: make --delete-existing-ruby in conjunction with --sharp-multi and existing-ruby options make sense

annogen Android apps: mode selector for sharpMulti + fix what happens if GOOGLE_PLAY_TRACK is set to empty string

Remove deprecated iOS browser app: the App Store stopped accepting UIWebView apps in April (updates are allowed till December but I think all existing annogen-influenced iOS apps use JS/Dart instead)

annogen Android apps: try to avoid other apps intercepting EPUB URL when we want it downloaded for annotation