Added tests to complete coverage on the following functions:
* CFE_ES_RunAppTableScan
* CFE_ES_ParseFileEntry
* CFE_ES_LoadModule
* CFE_ES_CleanUpApp
* CFE_ES_CleanupObjectCallback

The return code of CFE_ES_StartAppTask is a CFE status code,
so it should be compared to CFE_SUCCESS, not OS_SUCCESS.

Some FS API calls will pass through failure/status codes directly
from OSAL without remapping to CFE Status code values.

Note this behavior in the documentation and that it will likely
change in a future version of CFE.

Fix #1698, correct return code check

Fix #1599, documentation for FS APIs that return OSAL codes

Fix #469, Adding coverage tests for cfe_es_apps.c

Update notes to better clarify that the meta object must persist
for the duration of the dump operation, which occurs in another task,
so it must not be on the stack.

Also update documentation for background even callbacks to better
clarify arguments and expectations of the implementation.

Make sure functions documented as CFE status check for CFE_SUCCESS,
and functions documented as OSAL status check for OS_SUCCESS.

Add tests for
* CFE_TIME_Add
* CFE_TIME_Subtract
* CFE_TIME_Compare

Fix #1650, Add File Utility Functional Tests.

Fix #1659, Add custom epoch support to TIME UT

Update documentation for all command codes in CFE core apps, in
particular the error conditions, to confirm it matches the
actual implementation.

For common operations that apply to all commmands (length verification)
this is now put into the users guide as a general statement rather
than repeating the info in every command.

Fix #1702 #1709 #1713 #1717, Requirements update for Caelum

…_null_check

Fix #1718, Add null check to CFE_ES_TaskID_ToIndex.

Fix #1396, scrub command documentation

…onal-tests

Fix #1689, Add time arithmetic functional tests

Fix #1703, update docs for CFE_FS_BackgroundFileDumpRequest

Fix #1705, correct return code mismatches