Clean analysis termination

[aFrankLion]

• Use vexternaldb to cleanly terminate analyses at the end of an increment.
• New logger function for clean termination (log%terminate). log%error is still used for immediate termination of an analysis. log%error should still be used for dealing with input errors and numerical errors. Convergence errors should usually be able to use log%terminate without issue.
• Added a test which causes a DGD convergence issue in a single element. With the other changes in this commit, an additional output frame is generated. Previously, no data from the last model state would be added to the ODB file.

[TitanicEngineer]

Glad it worked :)