mouseable textedit and block mouse on dialogs

[laelnasan]

Changes to be committed: modified: src/ltui/dialog.lua modified: src/ltui/panel.lua modified: src/ltui/textedit.lua

makes textedit selectable by mouse and grabs mouse events on dialogs this prevents user selecting views in the background of the focused dialog, causing errors.

• Before adding new features and new modules, please go to issues to submit the relevant feature description first.
• Write good commit messages and use the same coding conventions as the rest of the project.
• Please commit code to dev branch and we will merge into master branch in feature
• Ensure your edited codes with four spaces instead of TAB.

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• 增加新特性和新模块之前，请先到issues提交相关特性说明，经过讨论评估确认后，再进行相应的代码提交，避免做无用工作。
• 编写友好可读的提交信息，并使用与工程代码相同的代码规范，代码请用4个空格字符代替tab缩进。
• 请提交代码到dev分支，如果通过，我们会在特定时间合并到master分支上。
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[waruqi]

Thanks!