Adds invoke script for automating release tasks (#324)

tasks.py

@@ -0,0 +1,27 @@
+"""Invoke tasks for building the app"""
+
+from invoke import task
+
+
+@task
+def clean(c):
+    """Clean flutter build"""
+    c.run("flutter clean")
+
+
+@task
+def translate(c):
+    """Update translation files"""
+    c.run("cd lib/l10n && python collect_translations.py")
+
+
+@task(pre=[clean, translate])
+def ios(c):
+    """Build iOS app"""
+    c.run("flutter build ipa --release --no-tree-shake-icons")
+
+
+@task(pre=[clean, translate])
+def android(c):
+    """Build Android app"""
+    c.run("flutter build appbundle --release --no-tree-shake-icons")