Nightly commit. Working on how Dakota shows up in build system.

[#52020843]
Rework of top level CMake code related to Dakota. Changed BUILD_WITH_DAKOTA to REQUIRE_DAKOTA, and moved REQUIRE_DAKOTA to an advanced option to better reflect how Dakota is a standalone and optional tool.

Now, we always look for Dakota, but only complain about not finding it if REQUIRE_DAKOTA is set to true (as it will be for the continuous integration machines).

Also added version handling. Set the required version of Dakota to 5.3.1 so I can try out the new version with our unit tests.

As a later step, I plan to conditionally compile the analysisdriver unit tests that use Dakota based on whether Dakota is actually present on the system.

[#52020843]
Breaking analysisdriver unit tests up into those that do and do not require Dakota. Removing dependency on Dakota of unit tests for basic functionality. 
Removing "if CMake found a Dakota executable" as a wrapper around blocks of code.

[#52020843]
If REQUIRE_DAKOTA is not checked, analysisdriver_tests pass without recourse to "if there is a Dakota executable".

[#52020843]
openstudio_analysisdriver_tests passing with Dakota 5.3.1 and Dakota-build system interaction improvements.

[#52020843]
Adding version checking for Dakota to Ruby and RunManager finders.

[#52020843]
Removing no-longer-applicable comment.

[#52020843]
Fixing Ruby tests to use upgraded dakota finder.

[#52020843]
Fixing typo in comment.

[#52020843]
Merge pull request #391 from NREL/20130625_ETH_UpgradeDakotaAndDesignTestSuite_52020843_52019959

Merging #391