Allow testlogger to be configured independently for each task

[radarsh]

Test logger should be configurable for each task (of type Test of course) independently. So if a project has multiple test tasks, they should be able define different values. A typical example:

testlogger {
    theme 'standard' // global
}

test {
    maxParallelForks = 8
    testlogger {
        theme 'standard-parallel' // use a parallel theme
    }
}

task functionalTest(type: Test) {
    maxParallelForks = 1 // no parallelisation
    testlogger {
        theme 'mocha'
        slowThreshold 10000 // as my functional tests are normally slow
    } 
    
    include 'com/adarshr/gradle/testlogger/functional/**'
}

Currently testlogger can only be configured globally.