Add ktlint Kotlin linter via Spotless plugin

[etanshaul]

fixes #16

Spotless plugin (used in cloud tools for intellij also) has built in support for ktlint.

There are a few peculiarities that we can iron out as we go along:

• the IJ formatter doesn't seem to enforce the line length rule (even though the linter will fail since 100 char limit is part of the Android Studio style guide)
• The current settings can lead to some strange formatting (see the changes to SkaffoldUiResources in this PR). As far as I can tell this is correct Kotlin styling
• ktlint has some basic auto-formatting limitations: it cannot (yet?) auto-format indentation problems, convert wildcard imports etc.. The IntelliJ formatter / import optimizer can fix these though.

[etanshaul]

see the discussion here: Kotlin/kotlin-style-guide#15 (comment) w/regards to the formatting changes applied to SkaffoldUiResources. I agree with yole's comment, but looks like they went with it:

https://kotlinlang.org/docs/reference/coding-conventions.html#function-formatting

[etanshaul]

Here's the same rule in the Android style guide (which is the one we are following currently):
https://android.github.io/kotlin-guides/style.html#functions

[ivanporty]

Interesting with parameter list, but this shouldn't happen very frequently anyway.