Create a Debian apt package

[framps]

This change has major impacts the way raspiBackup was installed and maintained (upgrades and betas) until now.

Following areas are affected:

Work in progress (See here)

1. Installation

   1. raspiBackup code will no longer be installed with the curl ... | sudo bash command. The installation now requires following commands to be executed:
      1. Download the deb package and the signature file
      2. Download and import the gpg key from the package maintainer framp from github
      3. Install the package with apt
   2. A script raspiBackupInstall.sh will be provided which executes the three steps mentioned above. That's much more convenient and will something like curl ... | bash - Note the missing sudo !
   3. raspiBackup and raspiBackupConfig will now be maintained together and will have the same version number.
   4. The extension samples are installed all the time. Activation can be done with the configurator.
   5. Support to select between crontab and systemd timer will be dropped.
   6. At the end of the installation a message should mention raspiBackupConfig

2. Installer

   1. The current raspiBackupInstallUI installer will be renamed to raspiBackupConfig. The new config script will still allow to config the primary features of raspiBackup but the installation is no longer possible. A check whether an update or beta is available will still be done and an update can be triggered.
   2. raspiBackupDialog should be installable

3. Beta , release candidates and hotfixes See compareVersion.sh script in build dir for details

   1. There will be beta releases and release candidates
   2. Release candidates will get a version number addendum like v0.7.2.1~rc1, v0.7.2.1~rc2 and so on which allows to have multiple release candidates. They are updated automatically whenever a new release candidate is available.
   3. Betas will get a version number addendum like v0.7.2.1~beta1, v0.7.2.1~beta2 and so on which allows to have multiple release candidates. They are updated automatically whenever a new beta or release candidate is available.
   4. Hotfixes will not use apt. Files are published on an individual base as before
   5. A beta or rc should be revertible To be evaluated

4. Updates

   1. An update of raspiBackup is no longer triggered by raspiBackup.sh itself. It's either done with raspiBackupInstall.sh with some option update or initiated by the configurator.
   2. During update the config file may have to be mergend with new options. Not clear whether this should be done during installation or when the new raspiBackup.sh version starts the first time.
   3. An update should be revertible

5. Cleanup

   1. All generated files should be deleted with sudo apt remove raspibackup (e.g. the backup config files)