Allow title of "This" menu to be changed in properties

Supports nasa/MCT-Plugins#16 (change "This" menu to "File" for distribution using Scenario plugin)

The text used for the "This" menu is read from MCTProperties.DEFAULT_PROPERTIES, which in turn consults mappings from properties/mct.properties and Java System Properties (in that order). This allows an installation to override the text of the "This" menu by specifying it either in properties or via JVM args (or to do neither, in which case "This" remains the default.) 

1 Wrote or re-wrote unit tests (Y/N): Y
2 Ran entire suite of unit tests successfully (Y/N): Y
3 Verified bug fix with the replication steps in JIRA  or verified the implementation meets the requirement cited in JIRA (Y/N): N
4 Code coverage requirements satisfied (new code=80%, changed code=at least as high as existing) (Y/N): Y
5 Code review date and attendees: Code review by Pull Request
6 Describe potential impact on other areas of the code: Menus in housing
7 Describe any test prerequisites for this fix (e.g., restart the database): Specify mct.menu.this in properties/mct.properties
8 For bugs marked "Regression - Yes", describe the cause of the regression: N/A
9 Did you modify any pom.xml file? If yes, did you get approval from QA and PM? N/A

Note on 3 above: Feature described by the referenced issue is incomplete, but is supported by this patch (that is, behavior in MCT platform should appear unchanged to user - i.e. "This" menu should still be named "This"). Referenced issue will be addressed in the MCT-Plugins repository, but is facilitated by this enhancement.