Make improvements to the format for OpenMX

[shigeandtomo]

Dear developers,

I would like to make some improvements on the format for OpenMX.

1. Change the format name from openmx/out to openmx/md
2. Add the if statement to read geometry optimization trajectories
3. Add the if statement to check if the SCF calculation has converged

Thank you in advance.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 92.30769% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 83.32%. Comparing base (46a8952) to head (f0f694b).

Files	Patch %	Lines
dpdata/openmx/omx.py	91.66%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## devel #619 +/- ## ======================================= Coverage 83.32% 83.32% ======================================= Files 78 78 Lines 6841 6850 +9 ======================================= + Hits 5700 5708 +8 - Misses 1141 1142 +1 ```

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