Adding tests for the restart mechanics

[llaniewski]

This adds tests for the restarting mechanics for d2q9. Tests both vtk files as well as csv.

Also adds a simple tool for merging csv files from restart runs.

[codecov-commenter]

Codecov Report

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

Comparison is base (f7a0f5f) 43.23% compared to head (6da3bc1) 35.14%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #483 +/- ## ========================================== - Coverage 43.23% 35.14% -8.09% ========================================== Files 166 162 -4 Lines 7536 6621 -915 ========================================== - Hits 3258 2327 -931 - Misses 4278 4294 +16 ``` | [Flag](https://app.codecov.io/gh/CFD-GO/TCLB/pull/483/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=CFD-GO) | Coverage Δ | | |---|---|---| | [d2q9](https://app.codecov.io/gh/CFD-GO/TCLB/pull/483/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=CFD-GO) | `31.92% <ø> (+1.46%)` | :arrow_up: | | [d3q27_PSM_NEBB](https://app.codecov.io/gh/CFD-GO/TCLB/pull/483/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=CFD-GO) | `?` | | | [d3q27_pf_velocity](https://app.codecov.io/gh/CFD-GO/TCLB/pull/483/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=CFD-GO) | `?` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=CFD-GO#carryforward-flags-in-the-pull-request-comment) to find out more.

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