Remove built-in Lato font

[iissnan]

There are many issues with built-in Lato font ( #135, #137, #164, #167, #187), so I decide to remove the built-in Lato font and replace it by using Google font API.

But Google font API has the connection issue in China, so I have to do some additional things for this case. If language is set to zh-Hans, NexT will not use Google font API. And there will be a new setting use_lato_font, to manually turn it on/off.

That is to say, Lato font will be:

1. off = language: zh-Hans || use_font_lato: false
2. on = !off

[iissnan]

The default value of use_font_lato is true. So if you set language to something other than zh-Hans and you have problem with connection to Google Fonts API. You need to manually change use_font_lato to false.

[eurusd]

use_font_lato: false
是解决手机浏览卡顿吗？

[eurusd]

好勤快的作者，超赞。

[iissnan]

@eurusd 去掉了 Lato 字体，加载速度应该会快一些。另外一个就是，在有些场景下，英文字体显示不了的问题。

[mingmings]

@iissnan 👍

[flashlab]

@iissnan 国内可以用http://libs.useso.com/ 提供的镜像