Consolidate `SEINet` occurrence data from updated search query

[jasonratcliff]

Combined separate SEINet occurrence data sub-directories into single location:

> fs::dir_tree('data-raw/SEINet')
data-raw/SEINet
├── P.bellii
│   └── occurrences.csv
├── P.floribunda
│   └── occurrences.csv
└── SEINet.R

Update search to include additional taxonomic terms:

• Physaria bellii
• Physaria floribunda subsp. floribunda
• Physaria floribunda subsp. osterhoutii
• Physaria rollinsii