[Startup] Rename startup jar

Move executable startup jar back to top level of build, replacing platform-specific scripts (these had drawbacks - terminal appeared in background with a lot of log noise on Mac; could be unclear to users which script to use). Rename executable jar to "MCT.jar", per nasa/mct#241

```
 Wrote or re-wrote unit tests (Y/N): N
 Ran entire suite of unit tests successfully (Y/N): Y
 Verified bug fix with the described replication steps or verified the implementation meets the requirement cited (Y/N): Y
 Code coverage requirements satisfied (new code=80%, changed code=at least as high as existing) (Y/N): N/A
 Code review date and attendees: Self-review by pull request
 Describe potential impact on other areas of the code: Startup
 Describe any test prerequisites for this fix (e.g., restart the database): N/A
 For bugs marked "Regression - Yes", describe the cause of the regression: N
 Did you modify any pom.xml file? If yes, did you thoroughly document your changes and reasons? Y
```

No unit tests; changes are to build configuration, no changes to run-time code.

Rationale for changes to build are documented in commit messages.