Improve themes handling

- Store user theme in session
- Logged out users will keep their theme
- Add theme background color to web manifest and meta tag

model/session.go

@@ -1,58 +0,0 @@
-// Copyright 2017 Frédéric Guillot. All rights reserved.
-// Use of this source code is governed by the Apache 2.0
-// license that can be found in the LICENSE file.
-
-package model
-
-import (
-	"database/sql/driver"
-	"encoding/json"
-	"errors"
-	"fmt"
-)
-
-// SessionData represents the data attached to the session.
-type SessionData struct {
-	CSRF               string `json:"csrf"`
-	OAuth2State        string `json:"oauth2_state"`
-	FlashMessage       string `json:"flash_message"`
-	FlashErrorMessage  string `json:"flash_error_message"`
-	Language           string `json:"language"`
-	PocketRequestToken string `json:"pocket_request_token"`
-}
-
-func (s SessionData) String() string {
-	return fmt.Sprintf(`CSRF="%s", "OAuth2State="%s", FlashMessage="%s", FlashErrorMessage="%s", Lang="%s"`,
-		s.CSRF, s.OAuth2State, s.FlashMessage, s.FlashErrorMessage, s.Language)
-}
-
-// Value converts the session data to JSON.
-func (s SessionData) Value() (driver.Value, error) {
-	j, err := json.Marshal(s)
-	return j, err
-}
-
-// Scan converts raw JSON data.
-func (s *SessionData) Scan(src interface{}) error {
-	source, ok := src.([]byte)
-	if !ok {
-		return errors.New("session: unable to assert type of src")
-	}
-
-	err := json.Unmarshal(source, s)
-	if err != nil {
-		return fmt.Errorf("session: %v", err)
-	}
-
-	return err
-}
-
-// Session represents a session in the system.
-type Session struct {
-	ID   string
-	Data *SessionData
-}
-
-func (s *Session) String() string {
-	return fmt.Sprintf(`ID="%s", Data={%v}`, s.ID, s.Data)
-}