CI: Adds CI for Application Codebase

Fixes #13 (closed)

• Adds build step for application(checks if application is being built correctly)
• Adds lint step(nope, it is not static analysis check yet, but as of now breaks on serious warnings; does not check formatting)
• Adds gradle wrapper files to VCS, as they are needed to run ./gradlew assembleDebug, otherwise we'll have to do a custom install at CI that'll be an overkill
• Uploads APK & lint reports as artifacts for download

NOTE: The CI is not complete yet, work to be done:

• Format Kotlin & XML files using ktlint/ktfmt & prettier and impose strict formatting rules(All these are supported by spotless, see here: for ktfmt, for ktlint & for XML)
• Use spotless to apply formatting to application codebase in one shot(i.e., via running a single command: ./gradlew spotlessApply or ./gradlew sA) and run spotless check on CI too
• Run Integration test also on CI