Allow user to use m2e-embedded Maven as executable (not sure there's an equivalent for Gradle)

[scottkurz]

To start we should incorporate

1. Installations - particularly the "Embedded" default. In fact it might be good enough to only support this embedded option. Whether we go further or not we'll need to design the details of the precedence among m2e options vs. the existing LTE-defined options and discuss this on the DXDI call, etc.
2. User Settings - Global settings, user settings, local repository - I don't have the reference handy but I recall a user asking for this.

At some point we should take a look at the equivalent in Gradle/buildship.