Implement notification subcommands (#389)

- [x] enhance notification listing
  - add `--states` and `--type` filters
  - toggle per-user or per-repo listing via `--mine` flag
  - print more fields
- [x] add subcommands to mark notifications as read, unread, pinned, unpinned. operates on
  - all notifications matching the `--state` and `--mine` filter flags, or
  - a notification specified by ID.
- [ ] ~~add a `--fields` flag for notifications listing.~~ *not in this PR*
- [ ] ~~interactive mode~~ *not in this PR*. this would go well together with #324

fixes #243, fixes #155

based on initial work in #283 and #386, but opening a new PR for @6543 to review as I changed quite a lot

---

### ⚠️ breaking ⚠️
- `tea notifications --all` has moved to `tea notifications --mine`
- `tea notifications` now only works with the context of a remote repo.
  To run this outside of a local git dir, run either `tea n --mine` or `tea n --repo <my/repo>`

---

Co-authored-by: Karl Heinz Marbaise <kama@soebes.de>
Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Norwin Roosen <git@nroo.de>
Reviewed-on: https://gitea.com/gitea/tea/pulls/389
Reviewed-by: 6543 <6543@obermui.de>
Reviewed-by: Alexey 〒erentyev <axifive@noreply.gitea.io>
Co-authored-by: Norwin <noerw@noreply.gitea.io>
Co-committed-by: Norwin <noerw@noreply.gitea.io>

cmd/issues/list.go

@@ -13,6 +13,10 @@ import (
 	"github.com/urfave/cli/v2"
 )
 
+var issueFieldsFlag = flags.FieldsFlag(print.IssueFields, []string{
+	"index", "title", "state", "author", "milestone", "labels",
+})
+
 // CmdIssuesList represents a sub command of issues to list issues
 var CmdIssuesList = cli.Command{
 	Name:        "list",
@@ -20,11 +24,7 @@ var CmdIssuesList = cli.Command{
 	Usage:       "List issues of the repository",
 	Description: `List issues of the repository`,
 	Action:      RunIssuesList,
-	Flags: append([]cli.Flag{
-		flags.FieldsFlag(print.IssueFields, []string{
-			"index", "title", "state", "author", "milestone", "labels",
-		}),
-	}, flags.IssuePRFlags...),
+	Flags:       append([]cli.Flag{issueFieldsFlag}, flags.IssuePRFlags...),
 }
 
 // RunIssuesList list issues
@@ -52,7 +52,7 @@ func RunIssuesList(cmd *cli.Context) error {
 		return err
 	}
 
-	fields, err := flags.GetFields(cmd, print.IssueFields)
+	fields, err := issueFieldsFlag.GetValues(cmd)
 	if err != nil {
 		return err
 	}