Use context manager for locks

This MR modifies the GWDataFindApp methods to use the contextmanager syntax for acquiring/releasing locks, rather than the manual method calls. This is cleaner and more reliable.

changed milestone to %GWDataFind Server 1.1.0

added gwdatafind_server.app label

requested review from @duncan.meacher

assigned to @duncan.meacher

added 3 commits

• 6930c0fd...509e76a7 - 2 commits from branch computing/gwdatafind:master
• e441433e - gwdatafind_server.app: use lock context manager

Compare with previous version

approved this merge request

mentioned in commit 1a5927ac

merged