Geemap

**Improvements:**
- Add function for removing drawn features 130
- Add function for extracting pixel values 131
- Add function for interactive region reduction 35
- Add machine learning tutorials

**Fixes:**
- [Fix js_py conversion bug](https://github.com/giswqs/geemap/commit/6c0ebe4006d60f9ebb4390d0914400fc276e2c7d)
- Fix typos

**Improvements:**
- Add function for getting image properties
- Add function for calculating descriptive statistics (i.e., min, max, mean, std, sum)
- Add more utils functions

Improvements:
- Add support for publishing maps 109
- Add `find_layer()` function
- Add `layer_opacity()` function
- Update Readthedocs

Fixes:
- Fix duplicate layer bug

This is a tagged version of geemap for the [joss-review paper](https://github.com/openjournals/joss-reviews/issues/2305).