Fix #148, Add table access protections

[jphickey]

Checklist (Please check before submitting)

• I reviewed the Contributing Guide.
• I signed and emailed the appropriate Contributor License Agreement to GSFC-SoftwareRelease@mail.nasa.gov and copied cfs-program@lists.nasa.gov.

Describe the contribution
Scrub use of all table pointers and add access routines to get an entry from the table instead of dereferencing the array directly. This pattern allows easier verification that all access includes a NULL check.

Also includes some refactoring to support this goal. Notably this includes changing the bitmask used to track if an appmon entry is active or inactive.

Fixes #148

Testing performed
Send command sequence that caused failure
Updated unit tests to cover those cases

Expected behavior changes
No segfaults when accessing table data

System(s) tested on
Linux

Additional context
Strongly recommend follow up to continue consolidating code. This PR touches on some things related to #5 but there is a lot more to do, a lot of code is still repetitive and could be refactored. Also, many functions rank high in cyclic complexity. This reduces it slightly by breaking up some functions (e.g. HS_MonitorApplications went from 128 to 90 by breaking it up) but 90 is still too high. There is much more that should be done to make smaller functions.

Contributor Info - All information REQUIRED for consideration of pull request
Joseph Hickey, Vantage Systems, Inc.

[ddstewar]

Tested on VM, with the table removed as stated in the issue this corrects. the following event were seen in response to the HS_CMD_ENABLE_APP_MON command:

EVS Port1 1980-012-14:07:01.46084 66/1/HS 25: Application Monitoring Enabled
EVS Port1 1980-012-14:07:02.66392 66/1/HS 33: Error getting AppMon Table address, RC=0xCC000005, Application Monitoring Disabled

The system did not crash and the table was reverted to Disabled once the background task recognized that it could not be accessed.

Approved