Fix issues with proposal page

• Disable the next button on page 2 if offerer has not been selected
• Move the "Company missing" and "Research group missing" messages to modals
• Move the contact selection to the top bottom of the third page under roles.
• Do not allow to proceed if no company contact is selected (related to #407 (closed))
• Move the period selection to below other info
• Display periods if any are present for the course edition, also for projects (might need a model redesign by moving periods from internship to project)
• Remove the medical and technical supervisors from the internship form
• If possible, route back to the proposal page after joining or creating a company via the proposal page
• Automatic research group linking message looks like an error and not just an explanation
• Remove fuzzy search from join company modal
• Improve display of exclamation mark in the company join modal