Add SubscriptionFilter resource

[adam-daily]

This change includes all handlers and related files for the SubscriptionFilter resource.

Issue #, if available:

Description of changes:

Includes all related files. Passes current contract tests:

======================================= test session starts ========================================
platform darwin -- Python 3.7.4, pytest-4.5.0, py-1.8.0, pluggy-0.12.0 -- /Users/adaily/Desktop/RPDK/aws-cloudformation-rpdk/env/bin/python3
cachedir: .pytest_cache
Test order randomisation NOT enabled. Enable with --random-order or --random-order-bucket=<bucket_type>
hypothesis profile 'default' -> database=DirectoryBasedExampleDatabase('/Users/adaily/Desktop/LogsResource/logs-fork/aws-logs-subscriptionfilter/.hypothesis/examples')
rootdir: /Users/adaily/Desktop/LogsResource/logs-fork/aws-logs-subscriptionfilter, inifile: /private/var/folders/65/6x_3qk7x4jz51hrxvj9f36pcrmvn8f/T/pytest_p0e0l_we.ini
plugins: random-order-1.0.4, hypothesis-4.36.0, localserver-0.5.0, cov-2.7.1
collected 2 items

handler_misc.py::contract_check_asserts_work PASSED                                          [ 50%]
handler_misc.py::contract_crud_exerciser ^@^@^@^@PASSED                                              [100%]

==================================== 2 passed in 322.37 seconds ====================================

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.