AutoFrontlight plugin (#2941)

* Add AutoFrontlight plugin

* Add configuration to control autofrontlight feature

spec/autofrontlight_spec.lua

@@ -0,0 +1,48 @@
+describe("AutoFrontlight widget tests", function()
+    local Device, MockTime
+
+    setup(function()
+        require("commonrequire")
+        package.unloadAll()
+
+        Device = require("device/generic/device"):new()
+        Device.brightness = 0
+        Device.hasFrontlight = function() return true end
+        Device.powerd = require("device/generic/powerd"):new{
+            frontlight = 0,
+        }
+        Device.powerd.frontlightIntensityHW = function()
+            return 2
+        end
+        Device.powerd.setIntensityHW = function(self, intensity)
+            self.frontlight = intensity
+        end
+        Device.ambientBrightnessLevel = function(self)
+            return self.brightness
+        end
+
+        MockTime = require("mock_time")
+        MockTime:install()
+    end)
+
+    teardown(function()
+        MockTime:uninstall()
+        package.unloadAll()
+    end)
+
+    it("should automatically turn on or off frontlight", function()
+        local UIManager = require("ui/uimanager")
+        Device.brightness = 0
+        MockTime:increase(2)
+        assert.are.equal(Device:getPowerDevice().frontlight, 2)
+        Device.brightness = 1
+        MockTime:increase(2)
+        assert.are.equal(Device:getPowerDevice().frontlight, 2)
+        Device.brightness = 2
+        MockTime:increase(2)
+        assert.are.equal(Device:getPowerDevice().frontlight, 0)
+        Device.brightness = 3
+        MockTime:increase(2)
+        assert.are.equal(Device:getPowerDevice().frontlight, 0)
+    end)
+end)