Make minimal header of Raw consistent with Acq Data encoding size + type check for ISMRMRD encodedFOV

[alexjaffray]

I noticed that sometimes the encodedFOV in the ISMRMRD files is written in a way that gets automatically interpreted by MRIReco as an Integer tuple when creating RawAcquisitionData. This is then incompatible with the AcquisitionData constructor which requires the FOV to be of type NTuple{3,Float64}. I added a small type conversion for this. Also, the minimal header of the raw data when producing RawAcquisitionData from AcquisitionData should be consistent with the dimensions of the AcquisitionData.

[codecov-commenter]

Codecov Report

Base: 63.05% // Head: 63.05% // No change to project coverage :thumbsup:

Coverage data is based on head (b897b61) compared to base (9c9d141). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #134 +/- ## ======================================= Coverage 63.05% 63.05% ======================================= Files 8 8 Lines 249 249 ======================================= Hits 157 157 Misses 92 92 ``` Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=MagneticResonanceImaging). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=MagneticResonanceImaging)

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[tknopp]

looks good.