[VersionBump] 1.19.0, fairly late

The core plugins whose version was attached to GS's were reseted to 2.0.0.

2.0.0 was chosen as reset version for plugins because it is higher than
  the one that was set by inheriting GS version. Furthermore, it's a
  major change from prior plugin versioning system thus it also makes
  semantic sense.

Justification for version bump:

== GS ==
9a4ab31f26 1.19.0
c13b935201 1.18.3
c13b935201 1.18.2
18fc39d2cf 1.18.1
c083a8bcc2 1.18.0
e8783d46d0 1.17.1
d9a42550ff 1.17.0
1536d3ef29 1.16.0
c03ed457a6 1.15.0
d2e6519bad 1.14.2
fe411e8138 1.14.1
b17e0b4169 1.14.0
daa5f87fd4 1.13.0
d75b5d2f4a 1.11.7
f6dbf66983 1.11.6
6cf674f8f8 1.11.5
7845a09b34 1.11.4
e4d432295d 1.11.3
339204f1ee 1.11.2
a4e679a118 1.11.1
7967db6ff5 1.11.0
bc030da320 1.10.1
9cc7df51d6 1.10.0
bf7f17474d 1.9.2
8a07edec5f 1.9.1
0042971d74 1.9.0
6b5450b7e6 1.8.0
5dcc98d1c6 1.7.0
e6667db0cd 1.6.0
3290227b50 1.5.0
a59c439b46 1.4.0
496ab8c920 1.3.10
986030060b 1.3.9
1d529c021a 1.3.8
f89c052cf8 1.3.7
38f2ecefac 1.3.6
e473937cb9 1.3.5
9a39ebe66f 1.3.4
ddc3cecfc0 1.3.3
2b43d484eb 1.3.2
e8e487187e 1.3.1

== Plugins ==
XMPP plugin
e0887220b0 bump patch
e186ad57d0 bump patch

OStatus
e186ad57d0 bump patch

Nodeinfo
ceae66a30f bump minor
586fb5a517 bump major
195296846e bump minor

plugins/VideoThumbnails/VideoThumbnailsPlugin.php

@@ -42,6 +42,8 @@ if (!defined('GNUSOCIAL')) { exit(1); }
 
 class VideoThumbnailsPlugin extends Plugin
 {
+    const PLUGIN_VERSION = '2.0.0';
+
     /*
      * This function should only extract an image from the video stream
      * and disregard any cropping or scaling in the resulting file, as
@@ -99,7 +101,7 @@ class VideoThumbnailsPlugin extends Plugin
     public function onPluginVersion(array &$versions)
     {
         $versions[] = array('name' => 'Video Thumbnails',
-                            'version' => GNUSOCIAL_VERSION,
+                            'version' => self::PLUGIN_VERSION,
                             'author' => 'Mikael Nordfeldth',
                             'homepage' => 'https://www.gnu.org/software/social/',
                             'rawdescription' =>