Return exception message back to client

[ManilShrestha]

Issue
Currently, if an exception occurs for a request, the server does not respond back to the client, causing the client to wait for the response back without ever receiving anything.

Fix
I have created a new function, handle_exception, which can be invoked in the catch part of a try-catch block. This function does the following:

1. Creates a packet response that is added to the responses and partial_responses queues.
2. Removes the prompt from the prompt_ids2jobs and prompt_length dictionaries, if they exist.

Result
This ensures that the client receives the exception message in the form of a response.

Note: Since this PR is created on top of PR #21, it also addresses Issue #18. Therefore, I will close PR #21 as this PR covers the code changes included there as well.