More lazy configuration

[mwos-sl]

Currently many things are initiated during configuration lifecycle phase. As a result applying the plugin extends configuration time of a whole project, which is a big deal for big projects with hundreds of modules.

Instead, as much as possible rsources should be calculated during task execution (e.g. in doFirst block).
Example:
ScoverageRunner is created always, even if none of scoverage tasks are invoked from the command line:
https://github.com/scoverage/gradle-scoverage/blob/master/src/main/groovy/org/scoverage/ScoveragePlugin.groovy#L83

[mwos-sl]

Same thing for:

def checker = new CoverageChecker(project.logger)

it could be easily moved to doLast { ... }