Only download IntelliJ if no local copy exists

[3flex]

When working with the SQLDelight project I seemed to end up with IntelliJ downloading every time Gradle ran its configuration phase which is a bit wasteful.

The overwrite flag does what you'd expect, while tempAndMove:

true if the file should be downloaded to a temporary location and, upon successful execution, moved to the final location. If overwrite is set to false, this flag is useful to avoid partially downloaded files if Gradle is forcefully closed or the system crashes.

[JakeWharton]

Alec?

[3flex]

The copy task is always run during configuration as well, unzipping even when the downloaded ZIP hasn't changed. It could be could be enclosed in doLast so the copy is done during execution phase instead of configuration phase. That also saves 10s of seconds on my (old) laptop every time Gradle's configuration phase runs.

[AlecKazakova]

yea looks good to me, try rebasing to pass ci