Remove unnecessary intermediate wxPanel.

There's no reason to have a wxPanel between the m_list list and the
containing splitter.  It seems to be a relic from the old days when
AttentionBar was grouped with it inside the splitter, rather than being
outside it.
Add barebones shell of the sidebar.

No real functionality yet.
Extract AutoWrappingText from ExplanationLabel.

Split the class into two: a base class that does the rewrapping and
updating, and a smaller ExplanationLabel specialization that adds
small/gray styling on top of that.
Move "auto comments" to the sidebar.

Remove text control for "auto comments" (aka "notes for translators")
from the main part of the UI and move it to the sidebar.
Remove TRANSLATORS: prefix from notes for translators.

This is not the only possible one, but it is a commonly used prefix and
one set by Poedit by default, so remove it automatically to get cleaner
look of the comment field, without useless noise.
Show comment icon in the list for auto-comment too.

Because the notes for translators UI was moved to the sidebar, use a
list indicator to highlight note's presence to make it more apparent.
Show previous msgid in sidebar info if present.
Move comments to the sidebar

Move translator's comments to the sidebar and show them underneath the
other automatic ones. This temporarily removes inline editing of
comments and only the toolbar button or Edit->Edit Comment can be used.
Make the sidebar nicer

Stylistic tweaks to make it look presentable. Use slightly blue
background, smaller font (on OS X) and separators between sections.
Align comments in sidebar with text controls

Align the comments, notes for translators and such so that they are
vertically at the same position as the source text on the left side.  If
there is room, that is: overflow above it if needed.

This makes it easier to read the comments because they are visually
closer to the area read by translators.
Fix string that should be wide to use L""
Fix typo: correct spelling is "overridden"
OS X: Fix crash when text control is empty

When reading the value of text control on OS X, empty text wasn't
properly checked for.
Better Sidebar API for adding blocks
Add Edit Comment button to the sidebar
Center the comment window on invoking button

If the Edit Comment window is shown form the sidebar button, center the
editable area on it, for easier access.

Not done on OS X, where the dialog is window-modal.
Don't call CatalogChanged() repeatedly

Don't notify PoeditListCtrl repeatedly about catalog changed, this is an
expensive operation that shouldn't be done twice while opening a file.
TM: return quality score with results

Instead of returning just the match strings, return a struct with
additional information.  Currently, only the quality score is included.

The score is approximated from Lucene's score, with scaling factor to
degrate it if a worse-quality match method is used.  Also ensure that
the best score of 1.0 is only ever returned when the match is exact,
i.e.  the source text is identical in both cases.
Make TranslationMemory::Get() thread-safe
Fix summary formatting of items with msgctxt

Don't accidentally duplicate message string when appending the context.

Fixes #102.