Call for Speakers: Show option below CfS instead of pop-up

[mariobehling]

Currently the CfS provides a pop-up. Instead of a pop-up show the options below the CfS:

1. Show info "No session have been submitted." (as long as there are no existing sessions)
2. Show the button "Add Speaker Details" (in the same way as of now, but below the CfS)
3. Show the option "Submit Session" also below the CfS, but if the user has not added speaker details yet, show an error message "You need to add your speaker details first before submitting a session".

[iamareebjamal]

Reproduction steps are given in the issue itself