Bump min version to PHP 7

Restore tinker command

composer.json

@@ -24,7 +24,9 @@
         "source": "https://github.com/octobercms/october"
     },
     "require": {
-        "php": ">=5.5.9",
+        "php": ">=7.0",
+        "ext-mbstring": "*",
+        "ext-openssl": "*",
         "october/rain": "~1.0",
         "october/system": "~1.0",
         "october/backend": "~1.0",

modules/backend/composer.json

@@ -16,7 +16,7 @@
         }
     ],
     "require": {
-        "php": ">=5.5.9",
+        "php": ">=7.0",
         "composer/installers": "~1.0",
         "october/rain": "~1.0"
     },

modules/cms/composer.json

@@ -16,7 +16,7 @@
         }
     ],
     "require": {
-        "php": ">=5.5.9",
+        "php": ">=7.0",
         "composer/installers": "~1.0",
         "october/rain": "~1.0"
     },

modules/system/composer.json

@@ -16,7 +16,7 @@
         }
     ],
     "require": {
-        "php": ">=5.5.9",
+        "php": ">=7.0",
         "composer/installers": "~1.0",
         "october/rain": "~1.0"
     },

modules/system/providers.php

@@ -20,6 +20,7 @@ return [
     Illuminate\Session\SessionServiceProvider::class,
     Illuminate\Validation\ValidationServiceProvider::class,
     Illuminate\View\ViewServiceProvider::class,
+    Laravel\Tinker\TinkerServiceProvider::class,
 
     /*
      * October Rain providers