Rails alerts do not need a col- class, they can fill the whole .row
Alerts displayed by angularjs error callbacks do not need a .col- class, they can fill the whole .row
Use Bootstrap CSS to hide the sidebar under the xs breakpoint (viewport width <768 px). Under this breakpoint the column for the entries occupies the whole 12 grid columns.

Not yet implemented: under the xs breakpoint, show a navbar button that hides the entries and shows the feeds/folders instead (at 12 columns), to select which folder/feed entries the user wants to read.
Reorganized alerts.

Now there's a single .top-alert in each page. Previously there could be two .top-alert divs in the read view; both were fixed to the page top, which meant they overlapped. Now all alerts are inside a single .top-alert and thanks to this they stack vertically.

Also a bit more rationalization, eliminating redundant divs and making alerts fill 12 columns at all resolutions.
WIP: Better organization of the sidebar markup, leveraging Bootstrap grid classes.
WIP: adapt sidebar markup to bootstrap grid for better responsive behavior.

Folder open/close link still looks bad with small viewport widths.
WIP: adapt sidebar markup to the Bootstrap grid classes for better responsive behavior.
Folder links in the sidebar now work as expected as viewport width changes (responsive!).
Better vertical alignment of elements in sidebar folder links.
Better vertical align of elements in sidebar feed links.
Better responsive grid behavior for sidebar feed links (the unread count badge no longer extends beyond the div).
A bit more space between icons and titles in the sidebar feed and folder links.
Better responsive grid for sidebar feed links at different viewport width breakpoints.
Better responsive grid for the "loading..." animated spinner that is displayed while loading entries.
Better responsive markup for start page.
Better responsive markup for start page.
Better responsive markup for the data import messages in the start page.
Start link in the sidebar now has the same height as the rest of links.
Better responsive markup for entries.
Hide "to read a feed click on it in the sidebar" message under the xs breakpoint.

For viewport widths under that breakpoint, there is no sidebar as such (it will be full-width and toggleable with a navbar button).