Fix test failures

a. `DeprecationWarning: The 'warn' method is deprecated, use 'warning' instead`
Updated call in `bumble/smp.py`

b. `ModuleNotFoundError: No module named 'bumble.apps'`
Updated imports in `tests/import_test.py`

c. Added `pytest-html` for easier viewing of test results
Added package in `setup.cfg`, and hook in `tasks.py`

d. Updated workflows to use `invoke test`

This is a partial fix of #81

tasks.py

@@ -53,7 +53,7 @@ test_tasks = Collection()
 ns.add_collection(test_tasks, name="test")
 
 @task
-def test(ctx, filter=None, junit=False, install=False):
+def test(ctx, filter=None, junit=False, install=False, html=False):
     # Install the package before running the tests
     if install:
         ctx.run("python -m pip install .[test]")
@@ -63,6 +63,8 @@ def test(ctx, filter=None, junit=False, install=False):
         args += "--junit-xml test-results.xml"
     if filter is not None:
         args += " -k '{}'".format(filter)
+    if html:
+        args += "--html results.html"
     ctx.run("python -m pytest {} {}".format(os.path.join(ROOT_DIR, "tests"), args))
 
 test_tasks.add_task(test, default=True)