Fixes the following warning:
```
CMake Warning:
No source or binary directory provided. Both will be assumed to be the
same as the current working directory, but note that this warning will
become a fatal error in future CMake releases.
```
* remove redundant "dtkwidget" in include directory;
* improve cmake, modify some variable names, use file() to collect
source files for scalability;
* add full target_link_libraries support.
Log: add full target_link_libraries support
Influence: all projects who include headers directly by path
Felix Yan
tsic404
guoyao
wangyixue
rewine
chenhongtao
justforlxz