Add CLI to dump environment and package info

Resolves #161

**Why this change was necessary**
It's useful to the user to have a CLI tool to dump environment info
into stdout to help ST contributors with debugging.

**What this change does**
Adds 2 helper functions to get environment information including OS
and CPU details, as well as resource usage.

**Any side-effects?**
New dependency is added, so the shimmingtoolbox package will have to
be reinstalled locally.

**Additional context/notes/links**
#161 (comment)

setup.py

@@ -35,6 +35,7 @@
         "scipy~=1.5.0",
         "tqdm",
         "matplotlib~=3.1.2",
+        "psutil~=5.7.3",
         "pytest~=4.6.3",
         "pytest-cov~=2.5.1",
     ],

shimmingtoolbox/cli/check_env.py

@@ -5,6 +5,10 @@
 
 import click
 import subprocess
+import os
+import platform
+import psutil
+
 from typing import Dict, Tuple, List
 
 CONTEXT_SETTINGS = dict(help_option_names=['-h', '--help'])
@@ -103,3 +107,63 @@ def get_dcm2niix_version() -> str:
     version_output: str = dcm2niix_version.stderr.rstrip()
     return version_output
 
+
+@click.command(
+    context_settings=CONTEXT_SETTINGS,
+    help="Dumps environment and package details into stdout for debugging purposes."
+)
+def dump_env_info():
+    """Dumps environment and package details into stdout for debugging purposes
+    by calling helper functions to retrieve these details.
+    """
+    env_info = get_env_info()
+    pkg_version = get_pkg_info()
+
+    print(f"ENVIRONMENT INFO:\n{env_info}\n\nPACKAGE INFO:\n{pkg_version}")
+    return
+
+
+def get_env_info() -> str:
+    """Gets information about the environment.
+
+    This function gets information about the operating system, the host
+    machine hardware, Python version & implementation, and Python location.
+
+    Returns:
+        str: A multiline string containing environment info.
+    """
+
+    os_name = os.name
+    cpu_arch = platform.machine()
+    platform_release = platform.release()
+    platform_system = platform.system()
+    platform_version = platform.version()
+    python_full_version = platform.python_version()
+    python_implementation = platform.python_implementation()
+
+    cpu_usage = f"CPU cores: Available: {psutil.cpu_count()}, Used by ITK functions: {int(os.getenv('ITK_GLOBAL_DEFAULT_NUMBER_OF_THREADS', 0))}"
+    ram = psutil.virtual_memory()
+    factor_MB = 1024 * 1024
+    ram_usage = f'RAM: Total: {ram.total // factor_MB}MB, Used: {ram.used // factor_MB}MB, Available: {ram.available // factor_MB}MB'
+
+    env_info = (f"{os_name} {cpu_arch}\n" +
+                f"{platform_system} {platform_release}\n" +
+                f"{platform_version}\n" +
+                f"{python_implementation} {python_full_version}\n\n" +
+                f"{cpu_usage}\n" +
+                f"{ram_usage}"
+                )
+    return env_info
+
+
+def get_pkg_info() -> str:
+    """Gets package version.
+
+    This function gets the version of shimming-toolbox.
+
+    Returns:
+        str: The version number of the shimming-toolbox installation.
+    """
+    import shimmingtoolbox as st
+    pkg_version = st.__version__
+    return pkg_version