Raise lint errors.

Change severity to error for unused namespaces, unused attributes, use
of deprecated resources, typos in string declaration, hard-coded sdcard
path in strings and not using newer versions of existing dependencies.

These cover some common mistakes in the prs submitted and will help
automate finding such errors thus making review process faster.

Author: Sam1301

app/lint.xml

@@ -13,5 +13,10 @@
         <ignore path="**/ic_person_24dp.png"/>
         <ignore path="**/ic_search_24dp.png"/>
     </issue>
-
+    <issue id="UnusedNamespace" severity="error"/>
+    <issue id="UnusedAttribute" severity="error"/>
+    <issue id="Deprecated" severity="error"/>
+    <issue id="Typos" severity="error"/>
+    <issue id="SdCardPath" severity="error"/>
+    <issue id="NewerVersionAvailable" severity="error"/>
 </lint>