Remove pybm report command, change pybm config list command

[nicholasjng]

This commit has two main contents:

1. The pybm report command is now removed in favor of pybm compare, which now has the report functionality baked in via an additional command line switch --absolute.
2. The pybm config list now prints the TOML file directly, simplifying from the previous logic.

Some more changes include:

• All pybm component classes are now fetched through a single API, get_component_class.
• The to_string() class method was added to the PybmConfig class.
• Builder and git wrapper were made class attributes of the environment store, removing some duplicated code.
• Some recyclable reporter tools were refactored into a new pybm.reporters.util module.

Bug fixes:

• Strip trailing newline from git commits obtained by the resolve_commit function, which previously appeared in the commit SHA written to the config file after checkouts.