Adjusts Forecast Output for 3D and 4D Applications

[RGNystrom]

Description

Added FourD yaml forecast option for 4D applications. When set to True the forecast output will be the subwindow frequency and when False, the default, the forecast output will be the window length.

The initial forecast output is also now retained instead of deleted.

Issue closed

Closes #280

Tests completed

Tier 1:

• [x] 3dvar_OIE120km_WarmStart
• [x] 3denvar_OIE120km_IAU_WarmStart
• [x] 3dvar_OIE120km_ColdStart
• [x] 3dvar_O30kmIE60km_ColdStart
• [x] 3denvar_O30kmIE60km_WarmStart
• [x] 4denvar_OIE120km_WarmStart_TEST
• [x] eda_OIE120km_WarmStart
• [x] getkf_OIE120km_WarmStart
• [x] ForecastFromGFSAnalysesMPT

Tier 2 (optional):

• [ ] GenerateGFSAnalyses
• [ ] GenerateObs