Use qualified ID

[punya]

Required for #129 (step 1 from https://plugins.gradle.org/submit).

[lptr]

Two things:

• we need to keep the old pride identifier as well for backwards compatibility (it is actually suggested by Gradle to do it like that somewhere, IIRC)
• the group name of the project is com.prezi.gradle.pride, I think the plugin's ID should match that. I'm not against changing to group name to com.prezi.pride, as the gradle part is not really clarifying anything, but it needs to be done at the same time.

[lptr]

Already fixed in master.