Move dplyr ahead in install_github

ggvis will fail to install because of insufficient dplyr version. Need to move dplyr ahead so it gets installed before attempting ggvis itself.
Merge pull request #147 from saurfang/patch-1

Move dplyr ahead in install_github
Always call attr() with exact=TRUE
Update data-hierarchy.Rmd

Should be `layer_text` instead of `layer_points`
Merge pull request #152 from saurfang/patch-2

Typo in data-hierarchy.Rmd
Remove unused prop_range function
Add register_ranges
Rename scale_ranges to scale_domains
Basic support for scales from data, for static plots
Add scale data support for dynamic plots. Also convert data_table to list
Remove unused function
Update test specs to use scale data
Rename register_domains to register_scale_domains
Switch from scale_domains to scale_info
Rename scale_domain.R to scale_info.R
Pull out scale_info so that it's reactive
add_default_scales: use list of static scale_info objects
Re-document
add_default_scales: simplify code
Use correct labels for axes