Build changes

[PatrykMis]

Description

• Migrate build logic to fully Kotlin DSL
• Update dependencies
• Set JVM target version to 11
• Update compileSdk, define buildToolsVersion
• Regression fix: Add verification of the downloaded Gradle distribution via SHA-256 again.

Type of change

Just put an x in the [] which are valid.

• Translation Contribution (non-breaking change which only adds or updates the translation to a language)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes.

• ./gradlew assembleDebug assembleRelease
• ./gradlew checkstyle

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

License:

• I hereby declare that all my contributions to this project is licensed using the GPL Version 3 License unless specified directly on source files

[allgood]

thank you @PatrykMis , please note that I am experimenting some changes on code, mostly on page detection and possibility to tune the image processing algorithms, so, I need to check if changes conflicts with my local branch. This looks good, but if it changes code of classes or manifest, I will not be able to merge.