added user_propsals to show all talks irrespective of conference

Checklist

• I have read the Contribution & Best practices Guide.
• My branch is up-to-date with the upstream master branch.
• The tests pass locally with my changes.
• I have added tests that prove my fix is effective or that my feature works(if appropriate).
• I have added necessary documentation (if appropriate).

Short description of what this resolves/which issues does this fix?:

• closes #1810

Changes proposed in this pull request:

A list of all proposals(talks) are shown on a single page irrespective of the conference Link to all_proposals are added to the navbar accordingly Withdraw and edit buttons are disabled if a user is not authorized to update a particular proposal