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/flags/csvflag.go

@@ -0,0 +1,49 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package flags
+
+import (
+	"fmt"
+	"strings"
+
+	"code.gitea.io/tea/modules/utils"
+	"github.com/urfave/cli/v2"
+)
+
+// CsvFlag is a wrapper around cli.StringFlag, with an added GetValues() method
+// to retrieve comma separated string values as a slice.
+type CsvFlag struct {
+	cli.StringFlag
+	AvailableFields []string
+}
+
+// NewCsvFlag creates a CsvFlag, while setting its usage string and default values
+func NewCsvFlag(name, usage string, aliases, availableValues, defaults []string) *CsvFlag {
+	return &CsvFlag{
+		AvailableFields: availableValues,
+		StringFlag: cli.StringFlag{
+			Name:    name,
+			Aliases: aliases,
+			Value:   strings.Join(defaults, ","),
+			Usage: fmt.Sprintf(`Comma-separated list of %s. Available values:
+			%s
+		`, usage, strings.Join(availableValues, ",")),
+		},
+	}
+}
+
+// GetValues returns the value of the flag, parsed as a commaseparated list
+func (f CsvFlag) GetValues(ctx *cli.Context) ([]string, error) {
+	val := ctx.String(f.Name)
+	selection := strings.Split(val, ",")
+	if f.AvailableFields != nil && val != "" {
+		for _, field := range selection {
+			if !utils.Contains(f.AvailableFields, field) {
+				return nil, fmt.Errorf("Invalid field '%s'", field)
+			}
+		}
+	}
+	return selection, nil
+}