Add edit-cache command to inspect and modify local cache

This edit-cache command is meant to be used during development to ease and speed up testing and figuring out issues. The key idea is to have an inspector and modifier of cookbook's status that pickle serializes/deserializes to/from both for build-tools.cache and linux_x86_64.cache (on Linux).

For maintainability it uses introspection to analyze the attributes of the RecipeStatus class, providing arguments to modify each of its members.

Usage:

usage: cerbero-uninstalled edit-cache [-h] [--bootstrap]
                                 [--steps [STEPS [STEPS ...]]]
                                 [--needs_build NEEDS_BUILD] [--mtime MTIME]
                                 [--file_path FILE_PATH]
                                 [--built_version BUILT_VERSION]
                                 [--file_hash FILE_HASH] [--touch]
                                 [recipe [recipe ...]]

positional arguments:
  recipe                Recipe to work with

optional arguments:
  -h, --help            show this help message and exit
  --bootstrap           Use bootstrap's cache file
  --steps [STEPS [STEPS ...]]
                        Modify steps
  --needs_build NEEDS_BUILD
                        Modify needs_build
  --mtime MTIME         Modify mtime
  --file_path FILE_PATH
                        Modify file_path
  --built_version BUILT_VERSION
                        Modify built_version
  --file_hash FILE_HASH
                        Modify file_hash
  --touch               Touch recipe modifying its mtime

e.g. inspecting a recipe's status

./cerbero-uninstalled -t edit-cache libffi       
0:00:00.001577 Loading default configuration from /home/pablo/.cerbero/cerbero.cbc
0:00:00.267447 Showing cache values for recipes: libffi
[libffi]
steps: ['fetch', 'extract', 'configure', 'compile', 'install', 'post_install'], needs_build: False, mtime: 1573815322.381322, filepath: '/home/pablo/Fluendo/fluendo-cerbero/cerbero/recipes/libffi.recipe', built_version: '3.2.9999+git~369ef49f71186fc9d6ab15614488ad466fac3fc1', file_hash: '80cd4a1c0feb7da8eab4862c30642b21'

e.g. modifying a recipe's status

./cerbero-uninstalled -t edit-cache libffi --needs_build True --steps fetch extract 
0:00:00.001619 Loading default configuration from /home/pablo/.cerbero/cerbero.cbc
0:00:00.253475 Modifying cache values for recipes: libffi
[libffi]
Before
steps: ['fetch', 'extract', 'configure', 'compile', 'install', 'post_install'], needs_build: False, mtime: 1573815322.381322, filepath: '/home/pablo/Fluendo/fluendo-cerbero/cerbero/recipes/libffi.recipe', built_version: '3.2.9999+git~369ef49f71186fc9d6ab15614488ad466fac3fc1', file_hash: '80cd4a1c0feb7da8eab4862c30642b21'

After
steps: ['fetch', 'extract'], needs_build: True, mtime: 1573815322.381322, filepath: '/home/pablo/Fluendo/fluendo-cerbero/cerbero/recipes/libffi.recipe', built_version: '3.2.9999+git~369ef49f71186fc9d6ab15614488ad466fac3fc1', file_hash: '80cd4a1c0feb7da8eab4862c30642b21'