add begin(port) to esp8266webserver, move some strings to flash, some refactoring (#4148)

* add begin(port) to esp8266webserver, move some strings to flash, some refactoring

* Moved more strings to flash, unified some strings

* move mimetable strings into a standalone file

* more string moves to flash, remove duplicates, refactor of template method, minor styling

* Reverted moving small string to flash (no heap advantage, reduces bin size)

libraries/ESP8266WebServer/src/detail/mimetable.h

@@ -0,0 +1,47 @@
+#ifndef __MIMETABLE_H__
+#define __MIMETABLE_H__
+
+
+namespace mime
+{
+
+enum type
+{
+  html,
+  htm,
+  css,
+  txt,
+  js,
+  json,
+  png,
+  gif,
+  jpg,
+  ico,
+  svg,
+  ttf,
+  otf,
+  woff,
+  woff2,
+  eot,
+  sfnt,
+  xml,
+  pdf,
+  zip,
+  gz,
+  appcache,
+  none,
+  maxType
+};
+
+struct Entry
+{
+  const char endsWith[16]; 
+  const char mimeType[32];
+};
+
+
+extern const Entry mimeTable[maxType];
+}
+
+
+#endif