[mod] load .config.sh from installation (utils/lib_install.sh)

**new** utils/lib_install.sh:
  Used to initialize installation procedures

  - Modified source_dot_config function that
    - loads .config.sh from an existing installation (at SEARX_SRC).
    - initialize **SEARX_SRC_INIT_FILES**
  - functions like:
    - install_log_searx_instance()
    - install_searx_get_state()

**modified** utils/searx.sh
    - obsolete environment SEARX_INSTANCE_NAME has been replaced
      by string 'SearXNG'.

**modified** utils/filtron.sh, utils/morty.sh, utils/searx.sh
  - source utils/lib_install.sh
  - normalize logging of environment variables using new function
    install_log_searx_instance()

**modified** utils/lib.sh
  - fix marginal typos

**Installation scripts**
  The utils/lib_install.sh is sourced by the installations scripts:

  - utils/searx.sh
  - utils/morty.sh
  - utils/filtron.sh

  If '${SEARX_SRC}/.config.sh' exists, the modified source_dot_config() function
  loads this configuration (instead of './.config.sh').

**SEARX_SRC_INIT_FILES**
  Array of file names to sync into a installation at $SEARX_SRC.  The file names
  are relative to the $REPO_ROOT.  Set by function init_SEARX_SRC_INIT_FILES().
  Most often theses are files like:

  - .config.sh
  - searx/settings.yml
  - utils/brand.env
  - ...

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>