Added checks on install

checks.py

@@ -0,0 +1,33 @@
+"""Checks to be performed before any install or upgrade"""
+
+import sys
+from urllib.request import urlopen
+
+from modoboa_installer import utils
+
+
+def check_version():
+    local_version = ""
+    with open("version.txt", "r") as version:
+        local_version = version.readline()
+    remote_version = ""
+    with urlopen("https://raw.githubusercontent.com/modoboa/modoboa-installer/master/version.txt") as r_version:
+        remote_version = r_version.read().decode()
+    if local_version == "" or remote_version == "":
+        utils.printcolor("Could not check that your installer is up to date: "
+              f"local version: {local_version}, "
+              f"remote version: {remote_version}",
+              utils.YELLOW)
+    if remote_version != local_version:
+        utils.error("Your installer seems outdated.\n"
+            "Check the README for instruction on how to update.\n"
+            "No support will be provided without an up to date installer!")
+        answer = utils.user_input("Continue anyway? (Y/n) ")
+        if not answer.lower().startswith("y"):
+            sys.exit(0)
+    else:
+        utils.success("Installer seems up to date!")
+
+
+def handle():
+    check_version()