refs: rename refs module to refdb
refs: rename branch view to refs view

Change the name of the branch view (as discussed in #257) in preparation
for enhancing the branch view to also show tags (issue #134).
refs: use refs_ prefix for internal methods and variables
repo: workaround empty --show-prefix output from certain git versions
argv: separate git log parameters from diff parameters

Parse of git log parameters and ensure they end up in %(revargs) rather
than %(cmdlineargs). This fixes use cases where tig is opened with some
search (e.g. `tig -SREQ_SCROLL_PAGE_UP`) and the diff view is opened
either from the main view or for example via the blame view.
options: enable graph when --graph is passed
main: use --pretty=raw format if reflog output is requested

This fixes a regression where `tig -g` would no longer show the proper
reflog messages.
main: fix segfault introduced in last change
view: remove refs and graphs from the view column enum

They are never shown independently so should not be exposed as a view column type.
draw: move view_columns_draw to draw module
draw: make methods only used internally static
refs: replace flags with reference enum type
refs: move ref format string lookup to separate method
refs: make reference formats configurable

This introduces a new `reference-format` setting and changes the default
reference format to make remotes a little easier on the eyes:

	set reference-format = [branch] <tag> {remote} ~replace~

Fixes #201
refs: show list of tags and use numeric sort order by default

Fixes #134
refs: update documentation to reflect branch view renaming
tigrc: revert unintended removal of stage-next

Removed by commit 0723f3b5079dd5def2f2854a54d5573028a24dfa.
view: fix drawing of ID column
search: show number of matches and the current match index
search: replace stage-next action with predefined search prompt command