Improve information-level output logging

[splatteredbits]

Some tasks don't implement any logging, so it is hard to see if/when/what a build is doing without verbose logging turned on. Update Invoke-WhiskeyTask to log when a task starts and finishes. The output should look like:

[00:00:20.73]  [GetPowerShellModule]
[00:00:20.73]  [GetPowerShellModule]  Installing PowerShell module BuildMasterAutomation 0.5.0 to .\PSModules.
[00:00:20.73]  [GetPowerShellModule]  Completed in 00:00:05.92.

If possible, it would be nice if future logging statements from a task didn't have the task name prefix and were indented four characters:

[00:00:20.73]  [GetPowerShellModule]
[00:00:20.73]      Installing PowerShell module BuildMasterAutomation 0.5.0 to .\PSModules.
[00:00:20.73]  [GetPowerShellModule]  Completed in 00:00:05.92.

If a task failed, replace "Completed" with "Failed".

Also, change the timespan prefix to only use minutes and seconds, not hours or milliseconds and default to two digit, non-leading zero hours:

[   20s]  [GetPowerShellModule]
[   20s]      Installing PowerShell module BuildMasterAutomation 0.5.0 to .\PSModules.
[   20s]  [GetPowerShellModule]  Completed in 5s.
[ 5m32s]  [ATask]
[15m51s]  [ATask]  Completed in 10m29s