full rework / rename to crabbar

[faervan]

see #24 for the motivation

Conceptual changes

• subscriptions are separated from modules and named sources
• modules define the layout of elements inside view. They may depend on sources to get access to variable data.
• styles define extra attributes of individual modules, such as paddings, margins, fonts and font sizes.
• themes define the colors to use in the modules and the background of the windows
• windows are named configurations, defining the variants of the configurations defined above as well as general window settings (e.g. anchor, size, monitor).

• Multiple windows can be opened simultaneously and managed through the IPC with a built-in intuitive command line interface.
• All settings can be overridden at runtime through the IPC and the overrides are preserved for the entire lifetime of the daemon even when the original configuration from config files is reloaded.

Configuration

• Switch from INI to TOML and from the configparser crate to toml, toml-edit and toml-example, enabling seamless parsing using serde instead of doing things manually
• Split the configuration into "general configuration" (config.toml), "themes" (a themes directory where different color themes can be added and then selected and switched without updating/swapping the main configuration) and "styles" (a styles directory - like themes but storing things like gaps, size, spacing, fonts instead)
• Store default configurations in /usr/share/crabbar, as specified by the Filesystem Hierarchy Standard
• Finally finishing the template engine to allow full customization of how a module is displayed during runtime

Logging

Until now, bar-rs only logged it's output to stdout and stderr using println! and eprintln! and used the bar-rs bash script to write this output to a log file.

• Use the log crate and a fitting logging implementation (fern?) to have a more idiomatic logging approach

Running crabbar / Unix sockets

Currently a bash script is used to launch and kill the main rust binary. This made things overly complex in setting things up the right way.

• Use clap to parse cli arguments in the main app.
• Run crabbar as a daemon listening to commands send through a socket or as a oneshot app sending commands though that socket.

Miscellaneous

• Switch from my own, unnecessary faervan/iced fork back to pop-os/iced (This has been in the template_engine branch for months already)
• Rework the subscription logic so that the app is only updated as often as needed, saving cpu usage
  • Updates get cached and flushed in a configurable interval
  • Immediately required updates (e.g. if the window title changes) flush the cache and reset the interval

this will close #15 , close #17 and close #24