Add more controls (#71)

* add more ducking command

* fix current music command

* provide more controls, like pause, resume, clear.

* add more controls in the web interface

* refactored and improved:
1. move get_music_tag_info to util, and
2. refined logic related to it.
3. now playlist will check for tag info thus update_music_tag_info is
useless and was removed
4. add "add folder" feature to !file asked in #65,
5. fix bugs related to !file

* truncate file list if too long

* fixed several tiny bugs

* fixed several tiny bugs continue

* fixed several tiny bugs continue continue

* fixed several tiny bugs continue**3

* fixed several tiny bugs continue**4

* added !filematch command to add files that match a regex pattern.

* truncate long message

* fix web interface delete file issue

* refresh after delete file

* add regex to listfile command

* refactored command part, added partial match support for commands

* organized

* added random command

* typo

* typo

* Fixed many bugs.

* Added workaround for azlux/pymumble#44 to fix the memory leak.

* changed logging style.

* fixed bugs related to random and resume

* fix now playing

* fixed issue related to download

* fixed issue related to download 2

* fixed thumbnail issue

* fixed add url problem in web interface

* REFACTORED, turned db.ini into sqlite3 database.

* fixed remove song problem

* fixed radio get title problem. auto download if tmp file is deleted

* fixed current index not loaded from database

* fixed: order of songs loaded from the database

* fixed: some obscure bugs. beautified error of commands

* added a workaround for TerryGeng/botamusique#1.

* beautified

* fixed: channel not loaded in the config

* fixed: auto checked for updates

* fixed: mysterious bug: sometimes "now playing" string cannot be properly
displayed.
The real reason is: do use <br />, do not use <br>. I tried hours to
find out this.

* chore: unified debug messages that refer to music items

* feav: fetch ffmpeg stderr mentioned in #72, reformatted logs.

* fix: async download not working

* fix: async download not working, still

* fix: async download not working, finished

* feat: queue command: ▶current playing item◀

* feat: support more than one command prefix

* chore: added some WARNINGs into default config file to avoid people to touch it.

* refactor: packed all string contants into constants.py, just to avoid people messing it around.

* refactor: required by azlux. Added a configuration.example.ini to keep people away from configuration.default.ini

.gitignore

@@ -110,4 +110,6 @@ configuration.ini
 2019-07-27 22_09_08-radiobrowser.py - botamusique - Visual Studio Code.png
 
 music_folder/
-tmp/
+tmp/
+
+database.db