You should avoid to put classes and dependencies directly in the WEB-INF/lib without any consistent mechanism for doing that.
I suggest to use the APS SDK for creating custom extensions for APS. This SDK will give you the right dependencies for each APS version that you want to use. It will build the JAR, the activiti-app.war and the related Docker container with its own volume for testing and deployment purpose.
There are two different branches of this project APS SDK 1.x for APS 1.x and APS SDK 2.x for APS 2.x. You should use the latest version of the APS SDK 1.x that is 1.7.5, here the link to download the Maven project:
Read the documentation here:
The Docker plugin will deploy everything for you executing a single Maven command:
mvn clean install docker:build docker:start -Pactiviti-admin
For stopping all the containers run the following:
mvn docker:stop -Pactiviti-admin
If you don't need the Activiti Admin you can avoid to set -Pactiviti-admin in the command.
You will also find in the project a basic example of a Four Eyes process with listener and a task service with unit and integration tests! Feel free to ask more questions if you need.
Hope this helps