Rename "Database" to "Vault"

We decided on calling the state file the "vault" a while back. This patch makes
the naming consistent across the codebase. I left "DatabaseImporter" classes
alone, because I'm not sure what a better name for those would be.

app/src/main/java/com/beemdevelopment/aegis/vault/VaultFileException.java

@@ -0,0 +1,11 @@
+package com.beemdevelopment.aegis.vault;
+
+public class VaultFileException extends Exception {
+    public VaultFileException(Throwable cause) {
+        super(cause);
+    }
+
+    public VaultFileException(String message) {
+        super(message);
+    }
+}