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]

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 ⚠️

Additional details and impacted files

@@           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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[njzjz]

This might be good, as the old one has never been released.