Swap PluginRunner with TaskRunner

[petebankhead]

Minor changes:

• Use 'crop' rather than 'trim' with Tiler
  • Turn this setting off by default with PixelProcessor

Major change:

• Convert PluginRunner to TaskRunner
• Provide QPEx.createTaskRunner() and QPEx.createTaskRunner(int nThreads) methods

The reasoning is that PluginRunner no longer really makes sense as a name: the class rather represents a simple and generic way to run tasks in parallel. It's also more general than in previous QuPath releases.

The following script shows it in action:

def tasks = []
for (int i in 1..50) {
    int n = i
    tasks << () -> sleepyTask(n)
}

def runner = createTaskRunner()
runner.runTasks(tasks)

def sleepyTask(int n) {
    Thread.sleep(250L)
    println "I'm awake! And I'm task $n"
}

When run interactively, this should show a progress dialog (after a short delay). But when using Run for project it will switch to using a command line task runner, and not generate a new dialog of its own.

The number of threads can also be specified. For example, for single-threaded tasks we can use

def runner = createTaskRunner(1)

This is an easy way to provide a progress monitor for multiple tasks.