Android: Refactor MainPresenter.installWad

Also replacing a toast with a dialog so that you have proper
time to read the message.

Source/Android/app/src/main/res/values/strings.xml

@@ -329,6 +329,7 @@
     <string name="grid_menu_refresh">Refresh Library</string>
     <string name="grid_menu_open_file">Open File</string>
     <string name="grid_menu_install_wad">Install WAD</string>
+    <string name="import_in_progress">Importing...</string>
     <string name="wad_install_success">Successfully installed this title to the NAND.</string>
     <string name="wad_install_failure">Failed to install this title to the NAND.</string>