feat: edit user-generated content

[nicobao]

• allow users to edit conversations, opinions votes, and polls for X hour after the content was created (put 3h by default in the server configuration, if the value is 0 it means users can always edit without time limitation. Add a different configuration variable for each content to edit: conversation, poll and opinion. Vote can always be edited without time constraint, ofc it's different). For polls, editing will basically delete the poll and create a new one, it will not take into account the existing responses anymore. Remember we mostly implemented everything to allow for editing by using the _content tables. Polls may be a bit less straightfoward so if it 's too complex just drop it, it's not an important feature