Allow other apps to call FairScan to scan a document to PDF (#81)

* Intent for external calls

* External calls: start on camera screen

* Isolate captured images for each scan session

* Remove access to settings when called externally

app/src/main/AndroidManifest.xml

@@ -27,9 +27,12 @@
             android:theme="@style/Theme.FairScan">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
-
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>
+            <intent-filter>
+                <action android:name="org.fairscan.app.action.SCAN_TO_PDF" />
+                <category android:name="android.intent.category.DEFAULT" />
+            </intent-filter>
         </activity>
         <provider
             android:name="androidx.core.content.FileProvider"
@@ -42,4 +45,4 @@
         </provider>
     </application>
 
-</manifest>
+</manifest>