GitHub integration improvements

When creating a new issue prefill title, description from Sleekplan infos. For repository, automatically select first. Create mandatory fields if no issue is created because fields are not filled. If you click enter, all info will be lost. When searching for issue on Github, also give the possibility to read the description. Provide exit from Create or Search step. After an issue is selected, it would be nice to confirm this before linking directly, like save or link.