Add license notices

LICENSE.txt

dist/style/weui.css

dist/style/weui.min.css

gulpfile.js

package.json

src/style/base/fn.less

src/style/base/mixin/mobile.less

src/style/base/mixin/setArrow.less

src/style/base/mixin/setOnepx.less

src/style/base/mixin/text.less

src/style/base/reset.less

src/style/base/variable/color.less

src/style/base/variable/global.less

src/style/base/variable/weui-button.less

src/style/base/variable/weui-cell.less

src/style/base/variable/weui-dialog.less

src/style/base/variable/weui-grid.less

src/style/base/variable/weui-msg.less

src/style/base/variable/weui-progress.less

src/style/icon/weui-font.less