Summary:
edc_navigator can be resized. in order to prevent collision
between edc_navigator and file_browser, limit the size to half each other.
Test Plan:
1. Run enventor
2-1. Drag the bar between text editor and edc_navigator
2-2. Toggle edc_navigator using key F10
3. Check edc_navigator size is saved after restart envertor
Reviewers: Jaehyun_Cho, Hermet
Differential Revision: https://phab.enlightenment.org/D4439