gui: Fix compilation issue due to deprecated glib API

g_thread_init() and g_thread_get_initialized() are deprecated since GLIB 2.32

Signed-off-by: Dunrong Huang <riegamaths@gmail.com>
gui: Fix compilation issue due to deprecated gtk API

gtk_color_button_get_color() belongs to gtk2, but lwqq does not
support gtk2, so replace it with new API of gtk3.

Signed-off-by: Dunrong Huang <riegamaths@gmail.com>
msg: Fix segment fault

If the content user want to send is too much, lwqq will crash. This is due to
the limitation of  our content length (1024 bytes), which is very very stupid.

So I reimplement the related code using string by malloc() rather than string
array to fix it.

Signed-off-by: Dunrong Huang <riegamaths@gmail.com>