[mod] utils/.searx.sh: add commands: install [dot-config|init-src]

This patch implements two new commands:

install dot-config :
  - copy ./config.sh to ${SEARX_SRC}
  - implemented in new function install_DOT_CONFIG

install init-src:
  - sync files (SEARX_SRC_INIT_FILES) with ${SEARX_SRC}
  - implemented in new function init_SEARX_SRC()

new functions: verify_continue_install() and prompt_installation_status()
  These functions are used in installation procedures to get the status of the
  installation procedure.  The status is based on the existing function:

    usage: install_searx_get_state

        Prompts a string indicating the status of the installation procedure

    missing-searx-clone:
       There is no clone at ${SEARX_SRC}
    missing-searx-pyenv:
       There is no pyenv in ${SEARX_PYENV}
    installer-modified:
       There are files modified locally in the installer (clone),
       see ${SEARX_SRC_INIT_FILES} description.
    python-installed:
       Scripts can be executed in instance's environment
       - user:  ${SERVICE_USER}
       - pyenv: ${SEARX_PYENV}

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