Add option for Source and License Info for Speaker Images

[mariobehling]

Problem and impact

The speaker image does not display source and copyright/license info. Please add fields as follows right below the speaker image field
a) Author or Source of Image (Enable Markdown, So user can add links)
b) Image License or Copyright Info (Enable Markdown, So user can add links)

1. Organiser View
   

2. User/Speaker View
   
   Add the fields into the public view as well right below "Please do not upload files larger.."

Related to #13

[shishiro26]

I am intrested to work on this issue can u assign this to me @mariobehling

[mariobehling]

Hello, please go ahead and make a PR for this issue. We do not assign issues to new contributors.