[FIX] Data formats clarification

[nbeliy]

• closes #1713

Changes:

In common principles/image format, removed reference to Nifti, and removed Nifti specific content. Rephrased the rest.

In MRI, added Data format section with Nifti requirements.

To do:

• [x] To add your name, please edit our Contributors wiki and add your name with the type of contribution.

[nbeliy]

@bids-maintenance

Added explicit mentioning of:

• incompatibility of ANALYZE 7.5 files with BIDS
• Concatenation of multi-volume acquisitions (e.g. for 4D fmri)

I'm not sure that this is actual requirements from BIDS, can you confirm or dis-confirm?

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 87.93%. Comparing base (05f64ed) to head (7f15ae8). Report is 70 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1720 +/- ## ======================================= Coverage 87.93% 87.93% ======================================= Files 16 16 Lines 1351 1351 ======================================= Hits 1188 1188 Misses 163 163 ```

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[nbeliy]

@Remi-Gau , did you got news from maintainers meeting? Should I go with PET format too?

[nbeliy]

Added section for PET. Essentially a copy-paste of MRI, with a minimum-recommended version of dcm2niix, and additional sub-sections to better fit into structure of page.

I'll put specific remarks into a review of code.

[nbeliy]

Hi @Remi-Gau , just to know is there any developments on this merge request?

[nbeliy]

Hi @Remi-Gau, just wanted to tell that I will be away until 29 of July.