shell: Consistent default style

This PR normalize common styles in order to be used by utility prompt-toolkit. Plus few other clean up.

• A common style is shared from bliss.shell.pt.default_style
• This style can be adapted by beamline/session
• getval and print_html and textblock use now this common styles
• The colors from bliss.common.utils was moved into bliss.shell.formatters.ansi
  • Colors from bliss.common.utils still can be used
• A new documentation page was added shell_print