Rename Style Manager Dialog to Symbol Manager Dialog

[DelazJ]

Although the dialog manages symbol (edit, create, import/export), it's imho wrongly named Style Manager instead of Symbol Manager, potentially leading to confusion with layer style (in the documentation at least).
This PR replaces GUI items to display "Symbol Manager" as expected. It doesn't touch functions name given that I don't know if this could break any compatibility (and to hopefully have it committed into 2.14). I essentially think about:

• QgsStyleV2ManagerDialogBase in src/ui/QgsStyleV2ManagerDialogBase.ui (class and file name) into QgsSymbolManagerDialogBase
• mActionStyleManagerV2 in src/ui/qgisapp.ui into mActionSymbolManager
• openStyleManager function in src/gui/symbology-ng/qgssymbolslistwidget.cpp (and .h) --> openSymbolManager
• pbtnStyleManager --> pbtnSymbolManager in src/ui/qgsprojectpropertiesbase.ui (couldn't find if it is used elsewhere so didn't rename it)

Any other item that should be replaced?
Are these changes compatible with 2.x or should they be kept for 3.x release?

[nyalldawson]

I don't think this change is warranted... The dialog doesn't just manage symbols, it also manages color ramps. And in future it will be extended to also handle font styles.

Given this I think style manager is fine, and symbol manager would be misleading.

[DelazJ]

good point for Color Ramp. However, Font (markers) are exposed in the Symbol Selector dialog as symbol layer type thus as symbol.
Whatever, I think it might be convenient to have a special wording for this dialog and keep Style for layer features representation. I unfortunately have nothing to propose.

[nyalldawson]

Sorry, when I say "font styles" I'm actually referring to "label styles", not the font marker symbol. Another thing which relates is that at some stage I'd like to move the default color scheme page from the Options dialog across to style manager (it'd be a better fit there), so that's another non-symbol setting which would be present.

I'm not against renaming from "style manager", but "symbol manager" doesn't fit. And I can't think of a good alternative either ;)

[NathanW2]

I plan on adding support for saving whole styles in the future so we might need a name that covers both use cases.

[SebDieBln]

We had a small discussion on this topic in my PR #2638 and I would like to quote myself:

What actually bothers me is the ambiguity of the term style.

• Looking at the source, the style manager is initialized with a QgsStyleV2* style, meaning a set of symbols and ramps.
• A style is also something that defines how a layer is rendered, including labels, scale based visibility and other settings. This can be saved to a QML file.
• And style is also used as the name of a tab within the layer properties.

While adding new features is always nice, I would ask to do something about the ambiguity of style, too.

[yjacolin]

I agree with @DelazJ and @SebDieBln about this!

[nyalldawson]

I'll close this PR for now. We need to discuss this further on the UX list and find an agreeable replacement term before proceeding.