Add Newgrounds.com (#877)

* new source: NewGrounds

* add icons

* add search and search filters

* display toast when Adult Content was filtered (login required)

* better sorting filter; let user adjust description

* if playlist available treat as series

* make sure anime is part of series (not playlist or collection)

* remove hi_res image

* remove unnecessary comment

* add NSFW flag

* simplify episode url extraction

* adjust stats summary in description

* use baseUrl in Referer header

* eliminate the need for restart after changing preferences

src/all/newgrounds/build.gradle

@@ -0,0 +1,8 @@
+ext {
+    extName = 'Newgrounds'
+    extClass = '.NewGrounds'
+    extVersionCode = 1
+    isNsfw = true
+}
+
+apply from: "$rootDir/common.gradle"