Migrate to androidx

[JavierSegoviaCordoba]

• Upgrade Gradle to 6.6.1
• Upgrade Android Gradle Plugin to 4.0.1
• Upgrade all dependencies
• Added Material Components library
• Remove old/deprecated dependencies
• Extract some strings to values

[MarkoMilos]

This has been implemented as a part of the latest release (check out release 1.0.0)

I'm closing this MR.