Opensr-test

- Fractional Difference Index (FDI) key is now both `fd` and `nd`. In order to
avoid confusion, with Normalized Difference (NDI). They are in essence the
same index. This is the metric by default from now on.
- We change the .png by .gif in the README.md file.
- We update the `README.md` benchmark section, with the new results (SUPER-IX feedback).
- We add a colab badge in the `README.md` file.

- Fractional Difference Index (FDI) added to the distance metrics.
- Bug in the `plot_tc` function fixed.
- A new parameter added to the `display_ternary` function to control the bin count.
- Config initial parameters have been updated.

- Logo changed.
- The `lightglue` submodule has been replaced with a new package called `satalign`.
- A new example has been added on how to run `opensr-test` on synthetic data.
- The documentation has been updated.
- The harmonization module has been updated to include the `satalign` package.
- We have added two new datasets: `spain_crops` and `spain_urban`.
- We add a new plot function: `plot_ternary`.
- We add a new plot function: `plot_histogram`.

- Paper submited to the IEEE remote sensing letters.