A change by Android Studio.

Maybe this file should not be in git.
AndroidManifest.xml: Correct the authority for the ContentProvider.
Document: Add save(OutputStream).

* app/src/main/java/org/glom/app/libglom/Document.java:
  And reimplement save(filepath) with it.
SelfHosterSqlite: Add some more error checking.
Add new top-level Glom Systems list activity.
SelfHosterSqlite: Discover an unused database name.

Instead of hard-coding one name that is reused.
build.gradle: Increase the build tools version.
GlomContentProvider: Create the empty file (at _data for files/#).

* Otherwise we get a FileNotFoundException when trying to create the file
  via ContentResolver.openOutputStream().