refactor: Migrate library and demo to androidx library + code cleanup

[RofaeilAshaiaa]

• Migrated library module and demo module to use androidx and refactor
  the existing layouts and classes to use androidx.

• Pumped compileSdkVersion and targetSdkVersion to 29, buildToolsVersion
  to 29.0.3.

• Pumped gradle-wrapper to 6.4.1, gradle plugin to 4.0.0 and fabric
  plugin to 1.28.0 + adding the org.gradle.parallel=true property for
  faster build time.

• Removed the butterknife dependency from demo module because it's now
  deprecated and causes runtime crashes without any obvious reasons and
  replaced the current code with a simple call to findViewById().

• Returned PixelFormat.UNKNOWN from getOpacity() instead of 0, the raw
  value of this constant to avoid the error warning in android studio.

• Removed *.iml files from the project to avoid project configurations
  issues on different computers when opening the project (which they
  should have been ignored in .gitignore file in the first place).

• Removed Timber library from the library module because:

  1. it's causing crash on android 7.1 with this crash stacktrace
     java.lang.NoClassDefFoundError: Failed resolution of: Timber/log/Timber.
  2. the library should not include a logging library dependency in order
     to be a light weight library with minimum size effect on the app size
     that include it as possible.