add header and footer arguments to navbarPage
remove condition attribute from tabPanel

the tab content visibility needs to be the union of data-display-if and whether the tab is active (the currenty implementation makes it always visible when data-display-if evaluates to true)
Merge branch 'feature/navbar-header-footer' into feature/layout-cleanup
Merge branch 'feature/remove-tab-condition' into feature/layout-cleanup
remove panelWithSidebar (this scenario will be handled by more composable top-level pages)
rename tabsPosition to position
update NAMESPACE For removed panelWithSidebar
Race condition where clientData$singletons can be NULL

Reproduced in Shiny Server load testing.

Code reviewed by @trestletech
add fluid parameter to navbarPage to specify fluid vs. fixed layout
add hr tag to exported html builder tags
update NEWS
Merge pull request #324 from rstudio/feature/hr-tag

add hr tag to exported html builder tags
Merge remote-tracking branch 'origin/master' into feature/layout-cleanup
Merge remote-tracking branch 'origin/master' into feature/layout-cleanup
Merge pull request #320 from rstudio/feature/layout-cleanup

misc cleanup of new layout functions
fix incorrect ellipses arg in hr function
Rproj changes: don't roxygenize; use --as-cran for test
Merge pull request #328 from rstudio/feature/rproj-changes

Rproj changes: don't roxygenize; use --as-cran for test