Add lint baseline, enable linting on CI, fix some reported errors (#3291)

This PR:
- fixes some errors reported by `gradlew lint` and the Android Studio "Code Inspection" tool
- adds a snapshot file `lint-baseline.xml` of the remaining lint errors and warnings to be used by the linter as baseline
- adds a job for CI to run `gradlew lint` on every build

Reviewed-on: https://codeberg.org/Freeyourgadget/Gadgetbridge/pulls/3291
Reviewed-by: José Rebelo <joserebelo@noreply.codeberg.org>
Co-authored-by: Arjan Schrijver <a_gadgetbridge@anymore.nl>
Co-committed-by: Arjan Schrijver <a_gadgetbridge@anymore.nl>

.woodpecker/run_lint.yml

@@ -0,0 +1,16 @@
+steps:
+  lint:
+    image: codeberg.org/freeyourgadget/android-fdroid-tools:latest
+    commands:
+      - pwd #bump
+      - ./gradlew lint
+
+#when:
+#repo: Freeyourgadget/Gadgetbridge
+#branch: master
+#this doesn't work yet:
+#https://github.com/woodpecker-ci/woodpecker/issues/687
+
+when:
+  event:
+    exclude: ['cron', 'deployment']