The general idea is to move related things closer together, make related
directory structures more similar to each other, and name components
a bit more consistent. Specifically:

- Move all four Security Dashboard types' init functions to
  `ee/app/assets/security_dashboard/${TYPE}_init.js`.
  - By bringing all of these together in one place, it'll make it easier
    to see what's common between them, and will make future refactoring
    a bit easier.
- Simplify "pages" entry points for each dashboard type.
- Move Jest store specs so that the directory structures align with the
  implementation directory structures.
  - No Karma specs are touched, since touching/moving them generates
    Danger bot warnings/errors. It's best if they're migrated to Jest
    anyway in another MR.
- Move/rename the `CardSecurityReportsApp` component to
  `ProjectSecurityDashboard`, under the
  `ee/app/assets/security_dashboard` hierarchy.
- Rename the base `SecurityDashboard` from `app.vue` to
  `security_dashboard.vue`.
- Strip any `App` suffixes used on imported dashboard components.