Changes project dashboard tabs to sentence casing

Changes the nav tab titles on the project dashboard page (```https://gitlab.com/dashboard/projects```) from title casing to sentence casing.

Before: ![Screen_Shot_2016-11-26_at_11.17.23_PM](/uploads/a31c951cf83f7670acee778db9337be5/Screen_Shot_2016-11-26_at_11.17.23_PM.png)

After: ![Screen_Shot_2016-11-26_at_11.17.39_PM](/uploads/a0cb5f6b6771e6f5149750ea1e7beb02/Screen_Shot_2016-11-26_at_11.17.39_PM.png)

Closes #25002

See merge request !7774