Speaker add Speaker handling / components

[artifactdev]

We need speaker handling inside the application based on the pretalx api which for now needs to be mocked.

1. create service for getting all speakers and a single speakers information based on the pretalx api -> please mock the data which is retuned for now until we have working test instances of pretalx
2. add interfaces for speaker information and map them according to what comes from the pretalx api
3. add component which shows a list of speakers like shown in the Figma

• should show 3 speaker items in a row if there are more then 3 it should show a "show more button" which then opens like a accordion and shows all the other speakers. (include at least 4 mocked speakers)
• Figma shows normal and hover/focus state -> animate the states with css
• on click on a speaker item a new page with speaker slug as parameter should open with the speaker details(design needs to be created at a later stage but you can add the information there already) -> at a later stage this page should also include the talks / sessions assigned to this speaker