[Save All] Consolidate Save and Save All

This addresses nasa/mct#131 by renaming Save All to Save (or, equivalently, making Save function as Save All). Whenever Save is invoked, any changes to managed objects (such as changes made to activities within a timeline) are also saved. When no managed objects are present, Save simply saves the current object.

In addition, the case where some (but not all) objects can be saved is handled differently. Previously, Save All had simply been disallowed, but this is too restrictive when it is the only Save option. Instead, a dialog appears explaining which objects will be saved and which cannot be saved (similar to existing dialogs for Delete All, and Remove Manifestation.)

Finally, added an inheritance relationship between save actions (for This menu and for Objects menu) in order to simplify code (both are the same action; only difference is menu they appear under and objects they apply to)

```
 Wrote or re-wrote unit tests (Y/N): Y
 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): Y
 Code review date and attendees: Self-review by pull request
 Describe potential impact on other areas of the code: Save action
 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/A
 Did you modify any pom.xml file? If yes, did you thoroughly document your changes and reasons? N
```