Further organize `src/` files

[alancleary]

Just got out of a meeting where we discussed introducing a new class a web component: bulk queries. We've also been discussing starting to introduce visualization components. For this reason I think we need to add a couple new directories under src/ to group components by their classes. Here's an example file structure:

├── controllers
│   ├── index.ts
│   ├── lis-cancel-promise-controller.ts
│   ├── lis-dom-content-loaded-controller.ts
│   ├── lis-query-string-parameters-controller.ts
│   └── lis-slot-controller.ts
├── core
│   ├── index.ts
│   ├── lis-alert-element.ts
│   ├── lis-form-wrapper-element.ts
│   ├── lis-loading-element.ts
│   ├── lis-modal-element.ts
│   ├── lis-pagination-element.ts
│   └── lis-simple-table-element.ts
├── index.ts
├── lis-linkout-element.ts
├── models
│   ├── index.ts
│   ├── lis-alert-modifier-model.ts
│   └── lis-string-object-model.ts
└── search
│   ├── index.ts
│   ├── lis-gene-search-element.ts
│   ├── lis-publication-search-element.ts
│   ├── lis-qtl-search-element.ts
│   ├── lis-trait-association-search-element.ts
│   ├── lis-trait-search-element.ts
│   └── mixins
│       ├── index.ts
│       └── lis-paginated-search-mixin.ts
└── visual
    ├── index.ts
    └── lis-phylotree-element.ts