Move thermocapillary model to TCLB/overlay framework

[TravisMitchell]

• I moved the thermocapillary option of the phase field model to the TCLB/Overlay framework. This model was developed for a particular publication, but is not needed in the base repository.
• I added a list of common models to the README for new users. This can be added to and adjusted as new standard models for common physics/applications are developed.

[codecov[bot]]

Codecov Report

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

Comparison is base (6f0196d) 38.16% compared to head (6c63685) 38.18%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #503 +/- ## =========================================== + Coverage 38.16% 38.18% +0.02% =========================================== Files 181 181 Lines 8240 8243 +3 =========================================== + Hits 3145 3148 +3 Misses 5095 5095 ``` | [Flag](https://app.codecov.io/gh/CFD-GO/TCLB/pull/503/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/503/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=CFD-GO) | `28.02% <ø> (ø)` | | | [d3q27_PSM_NEBB](https://app.codecov.io/gh/CFD-GO/TCLB/pull/503/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=CFD-GO) | `32.12% <ø> (ø)` | | | [d3q27_pf_velocity](https://app.codecov.io/gh/CFD-GO/TCLB/pull/503/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=CFD-GO) | `27.34% <100.00%> (+0.02%)` | :arrow_up: | 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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