add activity indicator when configuring in reflow mode

For now pillow activityIndicator is used to draw animated waiting icon
at the upper left corner of the screen. So pillow service should be
enabled to use this feature, but eventually we should implement an
activity indicator that is independent of native system.

frontend/ui/reader/readeractivityindicator.lua

@@ -0,0 +1,43 @@
+require "ui/device"
+
+ReaderActivityIndicator = EventListener:new{}
+
+function ReaderActivityIndicator:init()
+	local dev_mod = Device:getModel()
+	if dev_mod == "KindlePaperWhite" or dev_mod == "KindleTouch" then
+		require "liblipclua"
+		self.lipc_handle = lipc.init("com.github.koreader.activityindicator")
+	end
+end
+
+function ReaderActivityIndicator:onStartActivityIndicator()	
+	if self.lipc_handle then
+		-- check if activity indicator is needed
+		if self.document.configurable.text_wrap == 1 then
+			-- start indicator depends on pillow being enabled
+			self.lipc_handle:set_string_property(
+				"com.lab126.pillow", "activityIndicator",
+				'{"activityIndicator":{ \
+					"action":"start","timeout":10000, \
+					"clientId":"com.github.koreader.activityindicator", \
+					"priority":true}}')
+			self.indicator_started = true
+		end
+	end
+	return true
+end
+
+function ReaderActivityIndicator:onStopActivityIndicator()
+	if self.lipc_handle and self.indicator_started then
+		-- stop indicator depends on pillow being enabled
+		self.lipc_handle:set_string_property(
+			"com.lab126.pillow", "activityIndicator",
+			'{"activityIndicator":{ \
+				"action":"stop","timeout":10000, \
+				"clientId":"com.github.koreader.activityindicator", \
+				"priority":true}}')
+		self.indicator_started = false
+		util.usleep(1000000)
+	end
+	return true
+end