New function for evaluating independent data and other minor changes

[wevertonbio]

• independent_eval: new function for evaluating selected models with independent data
• new_occ: new data example with independent records
• Add guide on how to use independent_eval() in model_exploration vignette
• New helper function (predict_glm_mx) for predicting GLM models using cloglog, response, cumulative, and raw outputs. Previously, we were using enmpa::predict_glm, which does not support the cloglog output type.
• 'Cloglog' set as default for predicting maxnet and glm models
• Removed 'leave-one-out' from the available partitioning methods.
• Export function extract_occurrence_variables() to extract variables for occurrences.
• Update colors_for_changes to return fully opaque colors instead of transparent
• Document data in inst/ext
• Update description and readme: authors order and links to vignettes
• Update background colors for the website (replace orange with blue)